It's possible that teens are only testing boundaries with these apps.
They're then placed in the appropriate peer group, where they can post to a feed, comment on others' posts, add pictures and chat.
They'll get notifications when other users near their geographic area join, and they can search other areas by cashing in points.
Although adults use these apps both for casual hookups and for scouting out more long-term relationships, they're risky for teens.
For starters, although many of the apps aren't intended for them, it's easy for savvy teens to get around registration-related age restrictions. Location-sharing increases the potential for a real-life meeting; less dangerous but still troubling is the heavy emphasis on looks as a basis for judgment.
And with so much of their social life happening online, teens feel comfortable using apps to meet people.