What is "enough" users? Seeing as you've been a member of this site for only 2 weeks, do you think you're setting expectations too high for an initial sign-up rate? It takes time for SEO and word of mouth to set in and get people talking and it takes even longer to develop a Q&A site with a good enough reputation to continue to grow. Think about it this way, there are over 8,000 registered users on this site. How many of their sites have you registered for? This isn't a dig on you, but merely pointing out that there are a TON of Q&A sites out in the wild, and you need to make sure yours sticks out amongst the crowd if you want to develop a large registration base.
Then you need to start thinking about registered users vs active users. Even this site has a bit of a problem retaining active users. Getting people to register is one thing. Getting them to stay and use the site is an entirely separate problem.
Do you have Google Analytics set up on your site to see what your capture rate truly is? Do you actually have the traffic making it to your site and then not registering, or do you just not have traffic making it to your site at all?
There are so many ways to answer this question, but it boils down to content and marketing. Trying to let Google searches do all the work for you won't work well. And make sure not to spam other forums trying to get people to come to yours. That typically doesn't work either. If you can get your friends to help out, and maybe get some of their friends to help with initial Q&A's, I think you'll find your site growing pretty well after a while.
