Here are some ideas . . .
(1) Start a blog (WordPress is the best I would say).
(2) Join a FaceBook group (I have made some honest friends through FaceBook groups. Not Psychiatric, but still).
(3) Text me. I know, I know...It sounds like a creeper but I always make the offer that I have unlimited texts and usually have my phone on me. Sometimes a few texts can help. It's just an offer I make people feeling they can't find a "friend" who understands.
(4) Find some Twitter feeds relating to Depression/BiPolar/etc and as they post click and see who responds and engage them in conversation.

Hopet these help.
All the best,
Matt S.