I own a forum, it is only 4 months old and I have a very good result already, ranking 208,032 in Alexa now.
My forum is a breastfeeding & parenting forum in Chinese language, there were nothing like this in M'sia b4, at least none in Chinese language.
I invite ppl from other forum, and I give them more freedom to speak than the other forum they used to visit.
I also invited a popular breastfed blogger, where she added a link to my forum in her blog, which attracts a number of ppl joining my forum.
Now I have a lot of loyal members who are addicted to my forum.