... I found the email address of the site's host, and I'm complaining directly to them: info@fictionpress.com

The spammer's accounts are here:
http://www.fanfiction.net/u/3066094/ReikiaRoseAlloul
http://www.fanfiction.net/u/1569295/Labrunum_Steelfang
And there's a similar case in the Regular Show section which may or may not be the same guy:
http://www.fanfiction.net/u/2965508/Ducreuxed

If this isn't dealt with soon, I'm gonna complain to the police. To make sure something does get done, I need anyone else who's had problems to email and complain, and also tell me about the problems they've had so we have evidence. Okay?