There's a national association representing REIAs, and they have some useful resources. They're at http://www.nationalreia.com/ClubPortal/ClubStatic.cfm?clubID=795&pubmenuoptID=21757
As for finding investors, network with others in your area who are dealing with investors: hard money lenders, some (though not many) Realtors, accountants, real estate lawyers. Each one of them will have a list of contacts. Try to involve those people in the club, and tap into their lists.
The clubs I'm involved with all market heavily themselves--on Craigslist, Facebook, Twitter, through groups such as BNI, and so on.
Also, get involved in some of your local real estate investment clubs. Here's a listing of those in Pennsylvania: http://www.creonline.com/real-estate-clubs/pa.html You'll find that although there's some competition among the different REIAs, there's also a symbiosis. Some cater to one type or level of investor; some to others.
Hope that helps.