Anthropologist danah boyd (uncapitalization hers) is the author of It's Complicated: The Social Lives of Networked Teens (Yale University Press). In May, she told reason three ways kids find privacy online.
1. Social steganography. The most common way teens find privacy is not by restricting access to content, but by restricting access to meaning. They encode what they're posting using in-jokes, song lyrics, pronouns, and references that outsiders won't recognize.
2. Super logoff. Even Facebook can be turned into an ephemeral tool if you deactivate your profile whenever you're done using it. All you have to do is pretend to delete your account and Facebook will give you the option to deactivate instead. When you're not activated, no one can search for you or leave messages for you. While this is not a common practice, it's pretty ingenious.
3. Switch, switch, and switch. Parents think that they're "cool" when they know about the latest, greatest app. But once they show up, it's not as much fun. As a result, plenty of teens are on the hunt for something that no one's ever heard of. They jump from service to service, looking for a place where they can be let alone.