Be a resource and expert on other forums and places and then people will naturally gravitate to your forum as they seek more information
If you have budget, you may use forum posting services yo have start-up posts then hire others to post in other forums with your link in their signatures.. Buy signatures in other related forums.
I do not think Hosting is a very cools biz. Needs investment and difficult to market without reputation.
I think web hosting is a cool business, one of the reasons why we are is because of web hosting. Saying it is cool is like insulting your mother... Lol, I was joking with the last line but you get what I mean. I think to promote your hosting forum you will need to SEO your site, nothing major, just make sure the pages can be easily found by search engines. Also, I would change the look and feel of your site, too many colors going, I would stick to 80 % white and rest of it can be complimenting colors. The colors to me are annoying and does not promote long visiting, just by looking at it hurts my eyes. this is my opinion bro, not trying to be rude. Best of luck!
try joining other forums related to you and advertise it there. or you could just hire someone who could post in your forum to make it look busy.
Most webmaster related forum will work. First off though, you need to populate your site with some content first.