The Fan Fiction Advocate
"Our group was created as an early warning/verifying system to help combat plagiarism. The primary focus of this group is to validate respectable Fan Fiction blogs, bloggers& verify known, respectable authors. This group gives some security to the fans who should know the story they're reading really does belong to the person writing it."
They have lists of verified blogs, authors as well as lists of known plagiarists and alerts about what stories have been plagiarized and when they are corrected. This would be a great place to let people know if you see a story that is copied from someone else and let people know. Though they only have 20 followers I think that if they could get a large community of people it would be that much more affective.
And as an avid reader of fan fiction and someone who holds all authors in high respect I think it is our duty to make sure the credit for stories only go to those who write them. And with all the web and different sights they can't watch everything, so its up to us to keep an eye open and keep people honest.
With that said, I know many amazing stories that weren't completed because of this problem and taken down or just left incomplete. Even authors have left and its heartbreaking. So not being able to have any legal standing on stopping this in fanfiction, we can at least let people know that we won't be passive and just let this continue.
So join me in following this blog/twitter and looking out for stories and authors.
-Ed