Originally Posted by jct us101 
none of them are posting anything.
They are probably joining just to see what is inside, and then determining that there isn't much to reply to.
You would probably get a better start by allowing browsing of your forum without joining.
I rarely join a forum just to see what is inside. Usually I peruse an open forum first to see if I find it interesting, and then join when I wish to reply within the forum.