When it comes down to it, to make a website succeed, you need to target a niche market, or offer something better then the other (and there are many) websites out there which are likely similar to yours. Advertising or perhaps having some sort of affiliate programs to earn sign-ups quicker may work in your favor as well. Finally, adverting, and patience, patience, patience. Not every website takes off and ends up having the success of Facebook. You simply need to set your own goals for what you want to achieve, and perhaps consult with an outside agency who specializes in affiliate partnerships or advertising to get more specifics that you can do to get more people singed up and active on your website.