Well, at EGW, I have to go out manually and ask people to join... but I develop a friendship with them so I can trust them. Hehehe. Only the best!
...You just have to wait for a forum to get big. Start the spark by getting a few friends. Soon, they go to other forums and tell them about your site, and eventually a "web" will bring in lots of people. Plus you must have something that is unique. Gamingforce has it's amazing selection of audio. And look where it has gone.
Trust me, I've done this forum thing for a very long time.