The comments were posted on ff.de (http://www.fanfiktion.de), where you have to change the default setting from logged-in-only to anonymous-reviewers-too. I did that because I linked to the stories from some other places and I didn't want to force people to get an account.

So far, all the "anonymous comments" I received were signed at least with a name (I can understand why you might not want to put your e-mail into the open), even if I couldn't find out more. But it really sucks not to know how to reach out to the commenter.