patience...
if you just set it up, then Search engines still have to index it and people to find it. I know what you feel, I had that problem with a french speaking forum I tried to launch, but since I was on a VPS server it was costing me too much for the lack of activity on it
(
and it was a forum about IT and Web design, so there was already tons of competition and high quality ones)
Word of mouth is a good place to start. If your forum is related to TVseries, then possibly post (not spam!) on tv serie blogs.