Here's what my mother did...and I'll TRY to do with my own kids:
Embrace him.
You might HATE him, but your daughter obviously needs something that he is providing her...and you know that when you tell someone, especially a teenager, that they CAN'T/WILL NOT do something...they'll do it just to spite you.
So, my advice is that no matter how much you can't stand him or think that he's wrong...embrace him. Invite him over for dinner, take them both to the movies, etc...a) you're daughter might not want to be around someone who you actually "LIKE", and b) you'll be around without seeming like you're "watching them".
By all means, have rules...that's our jobs as parents; to protect our kids (from others and themselves!).
Can you ask the school for help? Did he go to the same school? Is he being "truant"?
My dad had the conversation with me about freedom when I was a teen...basically, I had all the freedom I wanted as long as I was honest and I didn't do anything that required the reins being pulled in. Could you ask your daughter in a non-accusatory way what she sees in this "gentleman"? Maybe explain to her that you want to like him, he just makes you nervous, blah blah blah...and see where she's coming from?
I wish you all the luck in the world...and I don't look forward to my kids' teen years! :)