If you look at most forums, then you will see that there are very few posters...
Probably because there are no interesting topics, or because people do not have the time to post.
If there are more topics, then people tend to be more willing to reply..
For instance, if I look at my MSX-forum (The MSX-Xpress & Affiliates Forum) I noticed that in the beginning, there were very few members and very few posts...So I posted some myself and invited other webmaster to become (Super-)Moderators and asked them to post some interesting stuff themselves...
They linked to my forum, which increased the traffic. Because there were more visitors, more topics were posted, and because more topics were posted, more visitors came, and so on...
So I would suggest to get some more volunteers to help on the forum and to post more interesting topics yourself..
But try not to steal too much of my visitors

We got over 400 posts now so I think we are one of the largest MSX-forums on the web...
F.Slagter
The MSX-XPress {http://msx-xpress.fixato.nl}
The MSX-Xpress & Affiliates Forum {http://www.fixato.nl/msx-boards}