zach's list, a documentary about his final days. >> we wanted to build awareness. we wanted to direct people to the fund. so that is what kind of led us to do it. >> sobiechtairs. >> the producers enlisted some of zach's favorite stars including jason mraz. >> thank you, zach. >> when i heard "clouds" for the first time i felt it was one of the most important songs i had ever heard. rarely do you come across a song that is written with such purpose or written for something so purposeful. >> his purpose was to leave a powerful message behind. >> you want a leave a melody behind? >> yeah. it's kind of me always been there for them. like, if they keep singing that song throughout their whole life i'll be right next to them the whole way. >> zach sobiech died in may shortly after his 18th birthday. 1200 people gathered for his funeral and together, they sang "clouds." >> i know he was there and he was grinning ear to ear because it was beautiful. ♪ go up in the clouds because the -- >> days after his passing, "clouds" hit number one on itunes and on billboard's rock chart. the online documentary went viral as well. over 11 million youtube hits and still count

music, sports, family, the things most important to zach sobiech. >> zach loved sports.ferent kinds of sports. football, basketball. >> in august of 2009, 14-year-old zach sobiech went for a run that stopped him in his tracks. >> when came back, he said mom, my hip hurts. i took him in to the doctor. we had an x-ray done. >> unusually thought it was a muscular thing. >> exactly. so we went to physical therapy for two months. >> two months? >> yeah. it got worse. it got to the point where he couldn't bend over and tie his shoes anymore. it was that bad. finally, the physical therapist said, this isn't working. you need an mri. >> that's when doctors discovered a tumor in his left hip. his mysterious pain was caused by a rare form of bone cancer. >> only approximately 500 children and young adults are diagnosed every year in the united states with osteo sarcoma. >> despite the shattering diagnosis and chemo therapy, zach remained hopeful. >> he was determined that he was still going to do the things he wanted to do despite his cancer. >> we had a lot of hope. there were a