Lending money to friends & family

i would not imply his parents in the matter, nor anybody ese otherwise, you might look like a psycho. I would just drop by and leave a message that makes clear that he owes you money. If you start bad-mouthing him to everyone instead of confronting him, you will get a lot of people against you, not necessarilly because they agree with what he's done, but because they do not want to take any side and save themselves the trouble of getting involved (and I am talking from experience).

I sorry, but you agreed to help a friend out, you alreadly said that he was pretty screwed for cash, he wasn't able to pay you want he said, and now you're calling him a scumbag and seem hellbent on revenge of some sort. You don't seem such a great friend yourself.

Sound advice from Halloweenqueen, you'd be wise to follow it.
You've been taken for a ride and you probably feel embarrassed, let down and angry but don't let that suck you into slandering and libelling your friend or you might be thought less of. I'm not suggesting you do nothing. If you are talking to his mates/acquaintances about this problem why not ask them what they would do in your shoes? You will then ensure as many people know about his bad behaviour as possible. This might be a tactic to use if you want to contact the parents because whether they are aware of the behaviour or not, or care about it or not, parents usually defend their offspring come hell or high water.
Why is he behaving as he is now? He's probably overwhelmed by the situation and doesn't want to think about it never mind talk to you about it, and this may always be the case. Try putting yourself in his shoes and you might get and idea of what he's feeling like - don't mean you to sympathise, just be pragmatic because if you have some idea of what's going on in his head you'll better be able to predict what outcome all this will have: will you get some cash from him; will he try and destroy your reputation.
I think the bottom line is that you've learned one of life's more bitter lessons and you'll have to chalk it up to experience because teaching moral lessons to someone else is a tricky thing to pull off.

Someones signature says "If a friend borrows a tenner and you never see him again, it was probably worth it." Just don't let it colour your view of the rest of your mates.

Oh and revenge is definitely best cold..... Give it time - you'll get your chance.

I recall lending money, around £200, to a "friend", thankfully wasn't living with me though. I never saw it again, even although I have a note saying that they would pay it back which was signed by them. I put it down to experience and whenever someone asks me for money now I tell them no, even though it goes against my nature to see some who is down on their luck and to have to knock them back for a sub etc. I wouldn't lower yourself by kicking up about the money owed. What goes round comes round etc, I later discovered that this person I lent the money to took someone in like you did and they totally screwed them over financially and the person I had lent the money to ended up in deep !!!!!! with the local council. If you are looking to get even, then I would bide my time and discreetly keep tabs on him, if that is possible.