What do I do? Friend help, desparate?

Firstly, going all arsonist on their houses is both illegal and the wrong approach, so I would probably discard that idea. Secondly, to get back at these mean girls, you need to play smarter. Collect anything you have- nasty texts, facebook conversations, letters, etc and keep them. As hard as it is, you need to involve your parents in this- never underestimate the fury of a parent who feels their child has been hurt. After collecting all the stuff you have, take it to the school- not a teacher, the headmaster. What these girls are doing is bullying, harrassment, defamation and character assassination, and that is not ok. Make it known to the headmaster that if something is not done to fix this situation, you will involve the police. If he/she does nothing, take a copy of the harrassment to the police and they will deal with it. I was a victim of that sort of crap at school, and I ended up having to take it further than the school. No one should be subjected to that. And tell the mean girls that you have kept copies of all the letters/texts/facebook conversations/emails, etc and if they dont stop harrassing you, they'll be hearing from your lawyer (you dont even need a lawyer to say it, the threat of legal action is usually enough). You are so much better than the mean girls, who are probably just insecure, bored or are having problems of their own that they dont know how to deal with- as cliched as it sounds, its 9 times out of 10 the reason for taking their crap out on other people. Hope this helps, good luck :)