How do I promote a newly created social network for seriously ill medical patients, without "spamming" anyone?

[Truth E.]

The network is free to participate in. I am not making any money from it, at this very early point, and I am seriously considering doing it *without* money, that is, in the spirit of giving something back to the community. To that end, I won't ever charge for membership, and I also won't ever allow discrimination. I'm running it now on a free website, and of course that site puts a handful of google text ads on the homepage in one column, but that's all. I want to create a safe space where no one will try to "sell" anything to the patient, and where seriously ill medical patients can hook up with each other and strengthen community. Oh, and did I mention? I need free and/or *very* low cost ways to promote membership!