I was on a StarWars role playing forum... Its where I learned how to RP, so I knew how to do that before I came here.
A woman from the forum posted about a 'free mmorpg' I looked into it, but mostly joined because she was my friend and I was curious. She doesn't play anymore, her character's name was 'Tiera Qel' A diaboli female. And well, although she didn't stay around, I did.
There is a much longer and more detailed story, going into how I went inactive after a week, and then expanding into how UTM without knowing it, brought me back into PS.
I guess you could say it was word of mouth, the players themselves advertising.