For starters HCL, User_Name, and Terra Solidum are the only ones who have been part of my since the Start-up and all others joined after, a few were recent like you as well. Everyone else who was with me from the beginning either hasn't posted in ages or dropped out because they lost interest or couldn't keep up. Terra joined because he saw it in the sign ups and it must have interested him since he signed up. User_Name and HCL are friends so they knew about it that way. I post in the last poster thread where I told my friends they should join, I got HCL and my friend Lief from that. User_Name I told through VMs. Everyone else was interested when they saw it in the sign ups.
There should be a thread for advertising RPs, though that's how I got people to join mine. I didn't really do much. Part of the lack of SUs may be because school is starting and people will be more busy