Teamwork always take the lead. Hire a team to handle the content and few seo consultants to get quality backlinks.
Get a few friends to help you... Automate the process... OR just divide up your time and do it naturally.
Is this like a social networking site? Something like blogger or wordpress.com? If you have a social networking site, I would suggest buying some google adwords. If you are into video marketing, you can buy a spot on the home page of youtube. Think about how myspace and facebook got started. How did they advertise? And then follow their footsteps, but add your own twist.