Probably the best way to get people interested is to keep the roleplays active. The more we write, the more people will want to join up.
The problem with most roleplays is that a lot of folks join for a few weeks, lose interest and drop out.
Good role plays go for months, may not be as intense in the short-term but tell good stories and keep the players interested.
The better players will probably want to join the longer stories. That also means that for a good story you always have to be able to bring in new players, but figure a way that if people don't post, they can be weeded out of the story.
Thus the five days of posting. If you don't post for five days, you can be killed. Rarely happens but it's possible.