I agree that you should be friends before becoming cofounders. Cool idea. How could one find the hackers first, in order to let them know that there is such a event?
Post flyers, email the CS club, email the local Linux User Group, email the local freethought club. You should also have the events regularly and make sure you keep them fun so that word of the event permeates the community and the reputation is built up. You also really should be looking to have fun and socialize with geeks, not just find hackers by throwing a party for them. :)
