If you tell me where your interests or kink lies I may be able to steer you to a story/thread you might like to read and perhaps join.
The ones you see that are 'closed' are just for those involved in the thread. The others are open and it's just a matter of reading it so you know what's happening and then asking if a character you have in mind would fit in and be able to join in the story.
Of course an even juicier option is to start your own thread. If you make it juicy, fun and tantalizing there will be someone (or many others) to join in on your story/idea/adventure.