This message recently appeared in my webmaster tools account: "User-generated spam - pages from this site appear to contain spammy user-generated content."
The URLs that were cited do not even exist! There are millions of posts on our site. Our entire staff works just about 24/7 removing anything that could possibly be considered spammy.
Over the course of three months, we actually manually emailed over a thousand websites, and then repeated this process two more times. After that we submitted a disavow file to Google. Regardless of our extensive efforts, we have not been able to recover.
I recently emailed Google and appealed to them but I doubt anything positive will result. I don't know what more can be done, but I'd appreciate some feedback.
How PBG Would Handle This Problem