. ♪♪♪ david polgar: it's not an app on their phone anymore, it's their livelihood. withheir frien. it's how they see the world. that's a part that i don't think everybody has adjusted to yet. dr. niels wouters: we're really at risk of having generations of young people that have formed identities in response to something that a technology platform prescribes to be the new normal. avani: behind the shiny dance videos, the platform is leading people down dangerous paths. lauren hemmings: i'd like to think that i wouldn't have struggd with an eating disorder if i hadn't downloaded tiktok. anne longfield: my claim with tiktok is that they are harvesting huge amounts of data illegally without the consent of children or their parents. jamil jaffer: if you just look at tiktok in isolation, it seems innocuous. but it's really, it takes place in this much larger context of data collection, artificial intelligence, and a real effort by the chinese to consolidate influence in the region and across the globe. avani: tonight on "four corners," "tiktok." in a joint investigation