How does a a online community gain initial users prior to launch?

Web startups with the theme of a "community" as in let's say a Match.com, a roommate finding service or even this site for that matter....my question is how do they gain their initial users? I am referring to a small scale operation with small scale funds. Is that what Beta testing is, where a static URL page briefly details the future website asking for those interested to submit their info so that when the site is launched it already has users?? I am sure this is not the case, but the question I have is how does a website initially get a decent amount of users with profiles so that when the site is launched the visitors love the concept, but do not love that there are only 3 other active profiles and unbeknownst to them they are the sites founders. :D Those of you with expertise, please be kind enough to answer this lingering question for me. Thanks, Marcus.

Communities are usually started by people who are part of an existing one but not necessarily online. You should know there is a need before building the site.

A beta site would be at least a partially working site where the users provide feedback on how it works and recommend new features.

If you can't email 10 people you think would use your new site, I wouldn't start building anything unil you can find more interest. The few people you do know can be a base for spreading the idea assuming this is important enough.