To a new user, it'll look like there's some serious activity, and they'll join in.
I believe this is what Quora did.
Once you hit critical mass, you can start integrating the futures.
Let's say you want to create a "find a cofounder website".
=====Very Specific Example Here =====
For tech entrepreneurs, you might create a tool that helps with adwords or business development. Maybe a directory of similar startups in their niche & pre-typed business development sample emails.
For business entrepreneurs, maybe create a lean website testing quick app that will test if their idea is viable. Idk, fake pricing page, fake screenshot, and they'd put in their prices, features, and sales copy.
Maybe you can go even simpler and create one of those dumb quiz sites: Are you a tech cofounder or a business cofounder quizzes - make it funny and you can get email addresses on both sides of the coin. Just getting the email addresses alone can potentially help solve the problem.
Reframe your site so that you don't rely on the community to power it -- make it so each user can use the product to its fullest extent without a single other user.
We had this same problem during the early planning process for our (currently just my) startup. Ultimately we realized that we were looking at the problem the wrong way. Instead of making the tool community-powered, we made it individual-user-powered. This lets us be "successful" with far, far less users.
Obviously this probably won't work for your site, but maybe it's just a useful thought exercise.
Would also recommend checking out this HBR paper - Strategies for Two-Sided Markets. It's talk of the "money side" and "subsidy side" is quite good.
When looking at your community, find ways that you and your friends/cofounders can easily generate lots of hiqh-quality content. It's important to set the tone of the site when you're generating the content. If you make lots of spam or low-quality content due to time constraints, the site will get a poor reputation and new users will continue the trend of making bad content. So make sure you generate the content wisely from the beginning :)
Based on the licensing of it either: use it directly, quote and reference to it, approach the best contributors and offer to pay peanuts for their content, approach the site and pay for a bulk license.
Or just outright steal it and deal with the repercussions later :-O (It worked, albeit indirectly, for YouTube etc.)
Or if you wish to go the normal route, add an incentive. Free "pro" accounts to the top contributors, ad-revenue share (with a minimum payout set to something sensible, like affiliate programs, so you only deal with the best contributors). Or something as simple as a points system (works well at somewhere like HN & StackOverflow).
Once a given area/topic has a certain amount of information, it's then much easier to promote that area/topic with additional marketing and incentives.
(Please lead me not into humor temptation. Jokes of this sort are discouraged here and I hate when my other selves downvote me.)
I did gather a few links to previous discussions on this topic (and a couple of related articles) here: