Marketing for the initial community of a community-based startup

My team is soon to release a new website. Essentially, the site is a collaborative game that relies on the community to be sustained.

What are some techniques/ideas for gathering the initial audience to a startup that requires a community to be sustained? For example, StackOverflow/Wikipedia require the community for their site to succeed. How do sites such as these get their initial audience in order for the site to pick up steam?

And, to increase the challenge, we require the initial audience to be a fairly large group of people. We can't afford to have users slowly come to the site over the course of days.

Anyway, all ideas are appreciated.

That's a classic chicken and egg problem.

Of course, the right answer depends on the particular service you are offering. In any case, a common sense approach is to start with a private beta with a very small and friendly community (you + friends + family + coworkers).

Don't launch the website publicly nor spend any money in advertising yet. Just start with a friendly community, explain to them what you want to achieve, and ask them to "bootstrap" the service using it frequently. Of course it helps if you have a wide network of people you can ask too, for example because you write on a successful blog or in a frequented mailing list.

I would also go the extra mile and give them some gifts to use the service initially (Amazon/Starbucks card for instance).

When you are sure your small network of users is happy with the service, ask them to invite their friends using the usual "Invite a friend" feature.

Only after that, you can launch and spend money on advertising.

Get a little ammount of true fans in niche markets, such us fb, twitter, friends, fools and customers from other websites of your team.

However, to get this ppl engaged, you and your team should be the first ones to work hard and create quality content.

Hope it helps :)