I've always just called them forum roleplays, which I picked up from the first time I saw them.

I noticed there were a lot of irrelevant results when I tried searching, but yes, looking up a specific topic, type of RP, or fandom will help a good deal. It sounds like you're set already, but I figured I add a couple things people didn't already say.

[url=https://support.google.com/accounts/answer/465?hl=en]If you're looking for more RPs out there, and have trouble finding anything, I'd also advise (if you're using Google) to turn off Search History and/or delete it all. The link here will mention both.[/url] Google tracks all the things you search, and might be giving you results it [i]thinks[/i] you want instead of the standard ones. Which can be a problem in some cases.

[url=http://www.top-site-list.com/roleplaying]I found a list of "top RP sites" here. At least some, if not all, are forum wide - I checked Plague(zombie RP) and a couple others from there, and all were forum-wide.[/url]