Another good site is the lonely planet. They have forums and there are loads of people advertising for mates to go thailand with. And Travelchums is another good one, you can post messages on the boards there for people going the same place as you. hope you find someone who's going the full moon party, sure you'll have a good time anyway.
Cheers Fin;yeah I do use the Thorn tree.I actually came across another good one just earlier-its the Traveltalk page on the Rough Guide site-really professional and looks like it gets a lot of hits.