Use your best assets to pull the guys! I'm not thin, I've never been thin and I'm never going to be thin! I've never had trouble pulling really, just a matter of confidence. Now every time I walk into a room I think in my head, "I am the most beautiful girl in this room, everbody loves me" and my confidence goes sky high (not to the point of being arrogant and stuck up my own bottom!). It took ages to get to that point though because I had to overcome the fact that I looked different to everyone else. I wasn't stick thin or pretty so I used my brains and personality to show them what I had that these dumb blonde stick thin bimbo's didn't! I would talk with boys about football (you don't need to know much, just mention a team and they will rattle on at you for hours!), drinking and cars, try to get on their wavelength.
It's hard but try to exude confidence, it sounds to me like you are quite a shy person if you are standing there alone. Like somebody else suggested, why don't you go and talk to the boys first? You will be surprised at their reaction, but if they are mean to you just rise above it and tell them they aren't worth wasting your breath on and walk off!