[bicknergseng]

Total speculation driven by personal anecdotal evidence:

I think a lot of teens don't have a use for Facebook yet. Facebook is a pretty good tool for staying connected with people from high school and college and past jobs that you wouldn't see otherwise. Most teens are in high school with the same people from their jr high/gradeschool. They have smaller social networks, are focused on small groups of immediate friends, and have watched the kids a year or two older than them get in serious trouble for posting the stupid stuff teens do on the permanent social networks (Twitter, Facebook), and would rather use ephemerality (Snapchat) to avoid accountability.

[pessimizer]

Sorry, accidental downvote.

> They have smaller social networks, are focused on small groups of immediate friends

I think you're right about this - teens actually see most of their friends a lot. The majority of my friends live in different cities than I do. Facebook is clearly more useful for me than them.

[mastermojo]

In high school I used Facebook to share photos with friends and comment on them. Similar to what people use Snapchat and Instagram for now.