Can you provide me with some wise advice about this teenage daughter situation?

I’m sure this is a classic problem for all parents of teenage girls, but new for me. My daughter is 13 and has a crush on a really terrible kid. He claims to have had sex with several girls, has been to juvie a couple times, been suspended many times, and recently lit a fire at a bus stop. He was trying to get her to go out with him during the school year, and she was interested but wary. He grew tired and started dating her good friend.

I’m not opposed to my daughter having a boyfriend, but not this one. He lives in our neighborhood, and she’s actively trying to get his phone number from her friends. She’s going to have a facebook account soon and told my wife she’d like to talk with him on there.

She’s thinks about him a lot even though she intellectually knows he’s bad news. I know she’ll forget about him soon enough, and just want to keep them separated until then. I don’t want them to become facebook friends or communicate at all. How do I accomplish this without being too forceful? I don’t want to come down too hard and have her sneak behind my back. Granted she may do that anyway, but please give me some good parenting advice.