this is "nightline." tonight, 15 seconds of fame. with tick-tock. burning new ground on social media, and now, in the hot seat. the wildly-popular app, the center of an investigation by congress. why some say the platform beloved by teens, looking to make it big. >> i have 29 million on tik-tok. >> could be a threat to national security. plus, kamala at 20. the college debate star driven by purpose. >> she did the work. there was nothing given to her. and it was hard. >> kamala harris now running for president in 2020, and the inside look from when she was 20. how her past helped shape her

campaign today. but first, the "nightline" five. kerrygold has a taste so rich it can take you to ireland's lush, green pastures. where grass-fed cows produce rich, creamy milk for a truly delicious taste. kerrygold. the taste that takes you there.

good evening. thanks for joining us. it's the popular app taking over social media, short and punchy y videos uploaded to tik-tok.

with growing talk of security risks. here's will reeve. >> reporter: crazy stunts, coordinated dance offs, and of course viral challenges. welcome to tik tok. the app that is taking social media by storm. we went deep into this new world spending time with some of it's most popular creators. like baby ariel. meeting blanco brown, the voice behind one of its biggest hits. and following rising stars hoping for a breakthrough. yet amid all the fun are new national security concerns about tik tok's chinese ownership. including serious allegations of censorship. >> i think the fact that they're so tightly connected to china is a huge issue as they become more and more central to global culture. >> reporter: it's all part of a new digital landscape, built one snappy video at a time. if you haven't heard of tik tok,

you're not alone. >> for all the moms out there, what is tik tok? >> reporter: reese witherspoon needed a tutorial from her 16 year old son deacon. >> this is so embarrassing. >> reporter: to become a tik tok-er. she is just one of the millions of people who have discovered the app, which a mashup of clever short form videos, often set to catchy beats. >> why did it explode the way it has? >> every day you open it up and it's full of different memes or trends you can engage with. and it's really really addicting. >> reporter: ryan broderick covers web culture for buzzfeed. >> so some of the stuff is incredibly cinematic. some of it is just music videos. some of it's getting a teacher to dance with you in a hallway. it's kind of whatever kids can come up with and that's why it's so exciting but also why you can get really crazy really fast i think. >> reporter: ariel martin, aka baby ariel, has mastered the the t ipncing toonlee " ecting

or "who let the dogs out" and creating innovative performance art. >> let's talk numbers. how big are you? >> how big am i. i am -- i have, ugh i hate talking about this. i am twenty nine million on tik tok. >> how does that make you feel. >> i mean. i guess it's like it's a beautiful thing. i just want to express love and positivity and as much as i possibly can. >> reporter: she was one of the first to build a following on the platform back when it was still known as musical.ly. >> you have people like creating movies and tv shows and they're getting paid lots of money. and this is another form of that. it's a job. i mean, it's what i do. >> reporter: we met ariel at the grove in los angeles. at the new dominique ansel restaurant >> how did you realize you were good at tiktok?

>> how did i realize i was good at tik tok? i think everyone is good at tik. >> yes it can. i think everybody can be good at anything. >> reporter: she moved from florida to california as her tik tok fame opened doors for her in hollywood. she just landed a role in disney channel's "zombies two." and is launching her own music career. she's directing herself in her cover of lou reed's "walk on the wild side," an ode to acceptance. >> i want to direct movies one day so that's like my main goal, that's where i want to be in a few years. >> reporter: ariel is just 18 years old. her parents have supported her tik tok career every step of the way. >> in the beginning i remember going, oh my gosh. like first it was hundred thousand. hundred thousand people do you understand what that is. and now it's interesting because it's sort of what becomes normal. you know like that becomes like sort of like the new normal. >> reporter: so much of the content on tiktok is created by teenagers in their bedrooms. that intimacy and exposure could be fertile ground for ogling eyes and predatory comments.

it's something ariel is aware of. >> to what degree should people who use the platform feel safe about that sort of faceless interaction. >> i think that goes with anything really no matter what you do. be safe, tell people what you're doing, where you're doing, what you're doing, how you're doing it, where you're going, what you're wearing. >> reporter: tik tok says it is working to keep it's young user safe and just released these videos made by popular creators. showing how to do things like filter comments. block people. or report inappropriate content. tik tok is adamant that the platform is a joyful place. but they are not immune to the perils of the digital world. tik tok had to take down accounts related to isis. tik tok deleted the videos and

permanently banned the accounts. and the company itself. and the company itself. which is owned by chinese artificial intelligence startup bytedance is now being investigated by congress over allegations of censorship and improper data collection and storage. >> so i think tik tok is stuck in a really tough spot with the fact that their parent company is chinese because they're trying very hard to be a western app. but there are all kinds of rumors about how involved the chinese government is in the app. >> reporter: the company would noanswer our questions. >> reporter: the company adding the china does not control the content of tik tok in the united states.

>> our us team makes decisions that we see as best for the us market, and we are given the independence to do so. >> reporter: none of this is scaring away the droves of teens and young adults who are flocking to tik tok. >> i am asked all the time what is the magical ingredient to taking off on tik tok? and i always come back to the same thing. on tik tok you truly are celebrated for just being yourself. >> reporter: kudzi chikumbu is the director of the creative community at tik tok. he promotes creators like drea okeke, aka drea knows best. >> as much as it is fun and entertaining, it truly comes from a special place. and like that should always be cherished and held very safe. >> reporter: at it's heart, music makes tik tok tick. the biggest hit of 2019, "old town road," first blew up on tik tok. ♪ i got the horses in the back

"old town road," which fused hip hop and country, paved the way for more unconventional breakouts like blanco brown's "the git up." >> what a journey you've been on. how did you get here? >> man, i pulled up an suv. >> reporter: blanco brown has been making music his whole life, producing for some of the biggest names in the industry. >> i was always in the background, you know? afraid to be in the forefront. the nerves always get me and i really wasn't the greatest at singing because i did have the confidence. so, i mean, like, it's been a journey. >> reporter: he wrote "the git up," released this tutorial on the steps and a tik tok challenge was born.

>> what goes through your mind when you see people? being happy and joyful and dancing because of something you created. >> man, i get emotional like, um, oh, you know, i'm i'm holding back tears now, you know, and it's a surreal moment. >> reporter: "the git up" changed cameron campbells life too. the 25 year old posted this video of him doing the dance at this job at an indiana walmart and it went viral. >> one of my videos actually went viral. i just started blowing up after that and people started contacting me and saying would you model for aeropostale and all that stuff. >> reporter: now camodancer94 is one of the new faces of aeropostale. one of the brands turning to tik tok to find the next fresh face and reach its young users. they brought him to new york for this photo shoot where he did the dance that made him tik tok famous. >> reporter: we watch as the views pour in. the power of tik tok on full display.

>> it just keeps going. >> reporter: cameron has his quit his job at walmart to become a full time tik tok-er. hoping to reach the same heights as creators like baby ariel. he's blazing his own path in this digital world. up next, the 2020 contenders at age 2067. tricks to help hide my bladder leak pad. like the old "tunic tug". you know it, right? but i don't have to, with always discreet. i couldn't believe the difference. it's less bulky. and it really protects. watch this. the super absorbent core turns liquid and odor to gel, and locks it away. so i have nothing to hide. always discreet. for bladder leaks. only roomba i7+ uses two multi-surface rubber brushes. ♪

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♪ ♪ ♪ ♪ ♪ blow a kiss, into the sun ♪ we need someone to lean on ♪ blow a kiss, into the sun ♪ all we need is somebody to lean on ♪ ♪ ♪ presidential hopeful kamala harris is trying to make

history, as the first woman and woman of color to win the white house. now the "nightline" series, "the contenders at 20", a deep dive into the formative years of the california senator. ♪ kamala was attractive so, of course, a lot of the guys liked her. but she also had a reputation for being smart, you know. so if you wanna step to her, you better step to her sayin' somethin' important. >> she was always the one who was very even keel, not fazed and not in that "i don't care way," in a focused way. >> she did the work! there was nothing given to her. i mean. and it was hard. she was one to not let anyone tell her who she was.

>> all americans, we go forward together. >> i'd like to show you macintosh in person. ♪ purple rain ♪ purple rain ♪ >> my name is jill louis. and i went to college with kamala harris. it was a very interesting time when we were at college at howard in the 80s. the first african american woman became miss america. and it was an event because it was groundbreaking. it was something that we had never seen before. "the cosby show" came on during that time and the opportunity to see educated professionals in a functional family was a new phenomenon on television. to be coming of age in a time where you could see that possibilities were opening up. the horizons were broadening for women, for people of color, that, i think, was very important. do not listen when they say it

can't be done. howard taught me, as it has taught you that you can do anything and you can do everything. >> my name is dr. shelley young-thompkins, and i had the pleasure of befriending kamala my freshman year at howard university. on campus she was known for being a woman about business. she and i would be mistaken for, you know, professors, because we would have briefcases. you know? >> a lot of colleges, people may wear jeans or sweatshirts. howard was a school where people actually dressed up to go to class. our generation felt like if we didn't start right now, you know, that would be problematic for us. so i think we took ourselves fairly seriously. dancing was a huge part of our social life. so there was no event, no party that didn't involve dancing. we never went to parties to, like, walk around and talk and hold a beer.

people danced. that was -- that was the culture of our parties. >> my name is lita rosario and i recruited kamala harris for the howard university debate team. a lotta times, when males and females are in, you know, debates or spirited conversations, the men kind of, you know, use their physicalness to kind of make their point. and i saw that kamala that she didn't back down when they did that. that she proceeded to make her point. and it's funny because when i look at her on television today, i still see that character in her. >> there was a little girl in california who was part of the second class to integrate her public schools, and she was bussed to school every day. and that little girl was me. >> every school day of the year in berkley, the buses move approximately 3500 children across town.

>> my name is carole and i lived around the corner from kamala. kamala and i were bussed together from 1971 to 1973 to thousand oaks school. we met each other every morning at the -- at the corner of bancroft and browning in west berkley, and stood in line to get on the bus. berkeley began the bussing program because they thought that they should integrate their schools. and because the neighborhoods were so divided. to be able to be bussed and go into this other environment. it transports you into a whole 'nother little, you know, universe. it just expands your mind. i just remember her being happy. she would talk, sing songs. if the bus driver needed to say something and the kids were talking, kamala would make sure, you know, people tamped down so that everyone can listen to what the bu -- bus driver was saying. i remember her being like, sitting in the front of the circle. she was very attentive. she was paying attention. she wasn't talking. you know, some of the kids might be in the back talking. she was listening. she was listening to the story. >> had she not been bused, you know, her life could have taken

a totally different course. >> i recall her saying that she maybe wouldn't be senator if she hadn't had that opportunity. >> my name is stacey johnson-batiste. i've known kamala since we were about four and a half years old. the one thing that stands out is she's -- she's the friend that listens to you. >> kamala's mother is indian and her father was jamaican. >> she was part of a global conversation around race and identity at an early age. and i think that she had to learn how to become very secure within herself. >> she just really grew up in a very multicultural environment. but her mother raised her and maya as black women, 'cause that's what they were. and it was a very intentful upbringing, and -- and -- and kamala really, you know -- was proud of it.

shyamala, kamala's mother, was one of the leading scientists in this country, if not across the world, you know, for cancer research. >> and she really pressed upon kamala and maya to be great and be who you wanna be, and you define yourself and you define who you are. >> don't you ever listen and let anybody ever tell you what you can or cannot be. >> this girl who i stood in line with to get on a bus to ride up to the berkeley hills, in our little neighborhood, is running for president. i'm extremely proud. extremely proud. >> when you talk about what kind of impact something like this would have. when you're able to see someone come through those barriers, that frees not only yourself but generations. >> i'm so proud of her, beyond words.

>> she has never lost an election. she ran for freshman rep. she won. she ran for d.a. she won. she ran for attorney general. she won. she ran for senate. she won. she's running for president. and up next, the dad taking a stand in the stands. full of good cheer. we call it the mother standard of care. it's how we bring real hope to our cancer patients- like viola. when she was diagnosed with breast cancer, her team at ctca created a personalized care plan that treated her cancer and strengthened her spirit. so viola could focus on her future.

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finally tonight, cheer dad. it's hard not to miss keeley holland of yorktown, virginia. the dad cheering on his daughter. and boy, does he know all the right moves. proving it to the squad and to the crowd. i'd say a perfect 10.