I do so by having 20 different characters who go among other RP 'circles' (I obviously keep these characters' identities hidden from the general public

) and then drawing them all towards my other characters, often one of my 4-5 main characters, usually linking them together... It doesn't always work, but I find that those characters are inside several different RP groups, and now I just have to find ways to draw those groups together. I've succeeded in making myself part of many groups, now I just have to make all of those groups join. Meaning more characters might need to be made

EDIT: Also, as far as encouraging NEW roleplayers, any new person I meet, I tell about Planeshift's emphasis on roleplay. If they seem interested, and I do try to make them interested, I teach them proper RP etiquette [aka, the difference between IC and OOC, not to use acronyms/l33t speak/etc. as well as how to avoid godmoding and forcing actions (referred to as Power Playing in many forum RP sites)] and show them the commands, as well as sometimes briefly explain the settings and highly suggest they read at least the races and settings info, and usually suggest they read the history too (not always a 'need' technically, but still very helpful). Some turn out okay, most I rarely keep track of, some I notice leave.
EDIT 2: going back to the first paragraph, and example would be my very main character Farren, who is involved with all Duraza RPs for the most part, who is involved with Royal House of Purrty RPs, and who is involved with the RPs surrounding Eretelien and Nalelack. I try to sort of pull other people into those RPs, and also to pulls those RP 'circles' (yes, those are what I mean by circles) together. See, everyone tends to follow a certain group. You have Duraza, Lolitra, Eretelien, and many other people that RPers center around. Anyone who centers around me, generally they are part of my 'spreading'. I try to make the Rangers into a floating RP circle, we float around, as small as we are, and we try to be within as many circles as we can. We spread the RPs, we spread them to each other and interact with each other, introduce each other to other people, whom we then interact with, and grow. Now we just need to reverse the effect and pull everyone back to -US-. That way, we've collected them, now we retract together and bring them with us, and they all bounce into each other. Obviously, different time zones make this hard, as well as work, sleep, etc. That's why we need more people to focus on doing so. A majority of the common RPers make a few friends and stick, sometimes greeting someone else, or conversing with them, but rarely beginning to 'follow' them in RPs.