Just spitballing, but since his work is already copyrighted he already owns the rights, I would guess..This got me thinking.
If what you post becomes the property of Facebook, and Stephen King has a facebook, does Facebook own a piece of all Stephen's work he posts about? Maybe not to the stories themselves, but do they own the visuals that Stephen posts? A movie still, an artist's rendering, a photograph?
That could get pretty legally tangled I would think.
Moderator -- how does that work?