Actually, the best way to attract other members from the forums you frequent is to put a nice little banner in your signature that links to your own forum. That way, it catches the eye of the curious. Even then, you might get only a handful of new members over the course of a year's worth of posting at a site like this one, but that's more than you'd get otherwise, even if you blatantly advertised by posting new topics about it.
Instead of a place like this, your best bet is to find a forum or community with a large number of active users and a high turnover (i.e. people are always coming and going). That's about the only place blatantly advertising your site can have a positive effect, but the method mentioned above also becomes several times more effective, making it worthwhile if you want to attract members.
Really though, unless your forums cover something a bit more broad like a hobby (cars, computers, video games, cosplay, rom hacking, etc.) or some industry or trade (computer programming, sales and marketing, truck driving, running a bar, acting, etc.), chances are your forum won't attract a lot of people by virtue of being just a forum. You'll always be fighting an uphill battle just to get people to join.
I mean, if Z and I had just went and made a Chrono Series forum, it would've died a long time ago in obscurity. Nobody goes to Google looking for a Chrono Trigger or Chrono Cross forum, and if anyone saw a link for such a thing somewhere, they probably wouldn't have bothered looking.
The only reason this forum has members is because it functions as a part of the site. Without the site, there would almost never be any new members, and the forums would eventually stagnate and disappear, like every other Chrono fansite that stopped updating or removed their content and just left their forums running, or even like VGMix after they decided to drop everything and rewrite it from scratch.
And even with the site, the only reason we had an edge over the competition at the time is because the Wiki-backend made it a hundred times easier for us to create and edit our content, so we could update faster and more often. That eventually turned us into both an active hub and a giant archive for anything Chrono-related, which in turn kept the forums going even after all the analysis discussion died down.
Of course, now we benefit a lot from the "last man standing" effect, but you get the idea.
