The way I usually did it was contact Cipsoft and ask for permission to advertise it, and ask where I should advertise it. They don't always allow it, which is a bit of a pain. If it's a fan-made event, as a workaround you could ask several of your friends to each make a post on their world.
What I would also recommend is sending a message to a number of fansites, so they can advertise your event for you. It usually helps reach a crowd that spend a lot of time on the fansites, and those people tend to be more interested in events as well.