Advice for a Startup

As we are sitting at work today, the MoveThatBlock team is wondering how we could improve our traffic? I know these things take time but Facebook blew up really quick so how did they do it? Was it word of mouth? Or was it simply that they had something unique and the community had a need for it? But in any case, how do you get people to talk about your company so fast? I know I may just be impatient and a little biased because I love our site and I want it to grow so quickly! In just one year we already have 1.2million registered users which is great! But I would love it if we could take over the market share from Craigslist. I believe the only reason people even use that site is because it's the only site out there of it's kind. But now that we have came around, our site is much more professional and more appealing aesthetically so why wouldn't we be the more popular site? Is it because people are loyal Craigslist users? It is hard for me to believe that because for me their site is so hard to use and it has a lot of spam! Any thoughts? Or suggestions?