I have had this issue, as many others have. If your site requires a community to work, i.e. your site will take something from one user and give it to another, then you will need some form of entrance strategy. In this case, your user base won't slowly start building up on it's own, even if the idea and implementation is great.

You will have to do most of the initial leg work, whether you spook yourself as a "real user" or not is up to you.

Additionally, find the problem you are solving, and put yourself in the shoes of a user with that problem, how can you solve it without your site?

Hopefully this will lead you to some communities that are relevant to the one you are trying to create. Now you just need them to sell you your product, one by one, until the site's popularity does it for you.

You need an entrance strategy.