Recently, my kid won an iPod Touch. She is incredibly lucky. Upon arriving home, she immediately started downloading apps. Because it was free, she downloaded the beSeen app. Her overall review is it is probably best for kids 8-12. That being said, she is sitting next to me playing it right now.
She receives posts throughout the day from her fictitious beSeen friends. As she navigates the beSeen world, she gains new friends and the game gets harder. The correct choice on what to post and share becomes less obvious. In fact, she accidentally posted a picture of her beSeen character having a drink on the beach. She saw the beach picture without noticing the cocktail on the table next to her. She was also confused by the choice of posts for arranging to meet for coffee. She did not immediately recognize that two of the choices potentially revealed her location.
I do not know if beSeen will help her navigate an actual social network, but the app does make kids aware of potential real problems. If your kid is trolling for free apps, suggest this one.