You'll have to give more details, maybe describe an opening scene or common area that new characters could play off of in their opening posts. 

Also, you have two people already (myself and [@leopard wcue]). You may consider moving forward with just that for now and making an actual thread for this where you can go into more detail. Maybe create a character of your own as a character sheet example. 

I've started with only one other person before, and if the writing is good and the story is interesting, people will join.