I had this exact same issue; the youth at our church posts all events on Facebook, as does the girls Bible study group. All of my daughter's friends are on Facebook, and she felt out of the loop. She just turned 14, and she's very responsible and has a good head on her shoulders. However, her father & I decided that she doesn't need one, mainly because there are still too many psycho sickos out there that we would need to worry about. Those are things that we felt she isn't mature enough to deal with just yet.
That's why she can only have people she's met in real time as friends. And you can control the settings to make it pretty safe.
