I'm currently part of a team of three STs, including yagathai and thomas_molitor, running a Vampire LARP in Philly. The game is called VIGOR MORTIS and it's been going on since April of this year, having grown into a steady LARP from its roots as a one-shot at last year's PhilCon.
There is an LJ community already existing for the game: necrophilarp. There's some backstory amongst the entries and some other information about the game. If you have some interest or your curiosity is piqued, you can e-mail me for any further details, such as available characters, background, etc.
So far, the game has grown by invite, recommendation, and word of mouth. Knowing mamcdowell and several other folks on this list, I wanted to extend an invitation along through this community and bring new players in on a game that has some great players and a social atmosphere.
We're having a big year-end four session game at PhilCon during the weekend of Dec. 9th-11th. Our game is separate from PhilCon itself, but will be run from within the same area. This saves our players the obligation of having to spend the extra money on a PhilCon badge if they were hesitant to do so.
I look forward to hearing from you and meeting some new people in the gaming community.