I've gotten in touch with Cary Bass, who has in turn put me in touch with Notafish. Hopefully, If things go alright, we should have a chapter up and running before too long. In about three weeks there is going to be a "Wikimeetup" in philadelphia, and I think Johnny and myself are planning to advertise the idea of a local chapter to the local Wikimedians. If we can get some initial support for the idea, We can move to advertising more online, such as going through [[Category:Wikipedians from Philadelphia]], or even advertising at [[Category:WikiProject Philadelphia members]].
On Wikibooks, my home wiki, the users don't tend to announce where they live, although I have learned of a few members from around my area.
Besides attracting existing Wikimedians to our chapter, it's really our primary goal to reach out into the community and get new people involved. There are a few ideas floating around right now as to how to accomplish this, all of which have some promise.