New members are very hard to come by. You really need to stay on top of things and constantly work at it. You may try adding a little user bar with the link hidden in it for the forum, or if you are unable to do so at the places you go, put the link in your signature.
You also could make a site map and submit it through the Google Webmaster Tools. This will give you a better chance of getting their bots to crawl your site and index the pages.
Another thing to try is to affiliate with sites. If you want, make a button no larger than 88 x 32 and I can add it to the affiliates box on my sites.
And lastly make your site a place people want to visit. Make it fun and user friendly. I know one of the first things I do when looking at a new forum is to see how the members treat each other. If they are rude and callous, I won't join.