Perhaps if you were to start up a role-play after gaining at least two or three other participants to get the ball rolling you might be able to get more people interested. I was honestly enjoying the idea of participating in that space adventure RP you made about two weeks ago. It seemed like one of those things that would have taken off after a few IC posts between you me and shikaru. With some RPs you have to give people a taste of what they can expect. Say if we'd continued that idea despite there being only three people: eventually someone's going to get curious due to the number of posts and pop in for a quick glance, they like what they see and they may sign up. You might've even been able to alter that RP a bit so it starts with a trio of ragtag mercs that end up recruiting other crew members from other planets as time goes on, maybe making little story arcs out of it and making the RP more organic as a result. 

But I digress, my point is that despite success in the past you still occasionally have to give people a glimpse at what you've got going to refresh their memory of why you had such successes to begin with, as well as bolster their confidence in the idea that the RP they're looking at is something really worth joining.