http://www.dreamwidth.org is a good place! You make an account for your character and look around journals like http://bakerstreet.dreamwidth.org/ (NSFW RP prompts there sometimes, so be wary of that if it's not your jam).
I love Lovecraft! Oh and if thats your style, you should check out the comic series Locke and Key .
Amazing modern Lovecraft done with great art. Nominated for an Eisner no less.
As for my sci fi roleplay, I can sum it up pretty well with this outtake from Serenity
I would suggest a mobile app if that's an issue. I don't think Reddit mobile supports PM's.
I prefer Reddit is Fun if you use Android or BaconReader if you use iOS.
wow, that's not a user friendly interface. For Android, I use Reddit is Fun. It's a bit more streamlined and simpler to use.