Let’s just go straight to the point on how to be successful.
Definition of a forum
An online discussion group. Online services and bulletin board services (BBS’s) provide a variety of forums, in which participants with common interests can exchange open messages. Forums are sometimes called newsgroups (in the Internet world) or conferences.
Yeah the more it appears a lot of people are members of the forum, the easier it will be for you to get new members. Their are affordable services out there, you just have to look around. I would go for freelance people that are trust worthy.
2. Offer some incentives for members to post on your forums: $, points, free advertising, etc.
Once you have gotten past the initial inertia, you can then decide whether to continue offering incentives.
I think as long as it doesn’t aim at a very specific niche topic it’s nearly impossible to attract members to a totally new forum.
Especially for something like SEO where there already are several big forums with thousands of members.
If you still want to try I’d start with:
– getting friends to register
– creating many fake nicks and posts to make it look big
– do post exchanges with OTHER webmasters who have the same problems.