You won't get people to join an empty forum.
Why should I join?
What makes it better than this place?
I concur, not trying to bash your newly built forum, although above comments sound harsh, these are actually honest feedbacks for you.
I've seen successfully blog/portal's forums out there usually made great contributions before hand to the public, like Dave did in early days of eevblog with his videos, and imo that was quite a gamble too since nobody knows the future, but once the traffic picked up and had enough audiences, hopefully it will be self sustainable.
The bad news is since there is no guarantee even you're walking the same path, that it will yield the same result like Dave's, worst some people might perceived you as a copycat.
You should think very hard , creative and make your site unique, and usually needs a very serious commitment as well. Just making a nice looking forum, and expecting gazillion people to jump in there joining like crazy is just too unrealistic.
Also popping out here or there just "plainly" inviting people is just not good enough, and if you do that too often like blindly bumping up this thread just now few posts back, or even creating new one without any good reason, people will starting to ignore you, and once the moderators see your invitations are beginning to look annoying, I'm pretty sure it will be deleted like other ordinary spam thread, and probably they will show you the boot too.
My 2 cents.