Getting a new forum off the ground is very hard work, but not impossible. The trick is to make it look active as no one signs up to a forum where there is no discussion.
You could use a combination of things including paying people to post, offering something for free like a decent prize for the top poster after 2 months (you'll need to manage the spam though) and making several profiles yourself where you post and answer your own questions.
An active looking forum and lots of traffic is the key.