Every is working for the goal of being on #1 on Google. If you break down and do your advertising correctly you can achieve it quicker then others. Also great keywords help out. The best way to advertise a forum in my aspect is Directory listings and Article submission. and advertising on big forums.

Best regards,
Dangys

If you want people to signup, you can do the following:
-Makes ads on a big forum
-Post some nice posts guest has access to
-Post some even better posts in a members area
-Make a contest about the best post count, that will get your forum active, and improve your seo.
-Make an affilitate offer (if you dont want to pay $$ you can make some free vip group or something like that..)

I have some tips to get forums members.

Discuss it in friends circle.
Invite friends and people by email.
Popularize it on social community.
Make forum decent to attract user.
Post unique and quality post that can interact people.
A huge post in forums can attract user.
Reply on their forums can make active a user.
Email subscriptions when another member reply on post can make also active any member.