You have 5 friends and do not play alternate shot or match play games. You need to meet other players. These types of games give you that opportunity. Clubs are about community and common interests. People in real life join clubs to be around people that they like and enjoy spending time with. The same can be said for the best clubs on WGT.
As you play with others and create a rapport you can personally talk about your club, exchange ideas and even offer invitations. This is a better way than sending out mass invitations to strangers. You are able to weed out the chaff before you even start.
As the club grows, recommendations from members becomes the best tool to continued growth because the members already care about the quality of THEIR club. (You need to make sure that the members know it is not your club but theirs.)
Then it is necessary to have a program to keep interest high. In house tournaments and keggers come to mind as ways to keep members happy. ( Hmm, the frat boy in me is slipping out.) You get the idea.