I think there would be a need for a some kind party planner. Basicly just a
tool which would allow to sign up looking for a party or to get members for a
party. It shouldn't have to be too complicated. Probably some restrictions for
members joining the party should be there ie. you could set your party to be
open or you would have a choice to accept request. This way you could start
looking for members day or some hours before starting the actual party even if
it is some 1 - 2 h exping or something.