Usually, I start up a roleplay, or usually start it up as a large open build for people to join in for.
That can attract 3 or 4 people. Usually a single day is spent building. Since the people spent time on building, they come back the next day when the actual roleplay takes place.
That means I now have a built roleplay with 4-5 players. They then proceed to roleplay, maybe someone else joins casually, we have fun, make it a memorable day and then they come back as regulars.
It's actually a nice feeling to think that you've got regulars on your server, people who see your name on the server list and decide to pick it out of the many others that are there. Makes you want to make your server the most enjoyable for the loyal ones.
Although, occasionally things go so good and fun that you never hear the end of them.
(*cough*Canto Xe, Western*cough*)(*cough*Megaguy, Shattered Memories*cough*)
Anyways, I find that if I make my server as enjoyable as possible, I get a few people to stay and enjoy it regularly. Those people then have a nice nact for influencing other people to join and stay, mainly by just being really fun people who add to the server.