Youtube, twitter, bluesky, whatsapp? Every app with a social aspect will be used by teens. And no, tiktok is not "only for teens" or "specially targeted at teens", nowadays everyone uses it and creates content on it.
If you run (say) a restaurant, you get big spikes in business from TikTok videos in ways you don't get from Facebook or Instagram or others.
TikTok is the platform everyone is one right now.