Just go alone!
I've been to five full moon parties, three times alone, once with friends, once with my girlfriend.
When I went with friends, I lost them all, only to find them again at various times and places. They had mostly all lost each other, too.
When I went with my girlfriend, I literally held her hand for about 50% of the time and kept my eyes on her for about 90% of the time to make sure I wouldn't lose her.
When I went alone, I would meet loads of random people, only to lose them, and find them again, and so on.
The point is, basically, that it is very hard to stay together as a group at the full moon party. Doing so is really only worthwhile if it's someone you really want to spend time with, and even then you have to make a real effort at not losing them, something that gets harder as the party gets wilder and you get more intoxicated
Enjoy the party, it's unlike anything else!