Right now I have a hobby forum, which started out with me and three other guys posting, and we were all pretty into it. Then they got one of their friends to join, and then they told a bunch of people, and then through word of mouth the forum got to be a fairly popular forum... mainly because of us four being really dedicated to it. That is the approach that I would recommend.
Though it is financial mortgage and brokers forum I would suggest if you target related financial and real estate sites and forum you might get good traffic. You can also add few section in your forum like topics on money saving guideline, section on personal bankkruptcy and assistance, financial assistance/funding for new sites etc.