Personally, I tend to just call those "fake" accounts. Fake, in the sense that the person behind that account is someone other than who they are claiming to be

Personally, I tend to just call those "fake" accounts. Fake, in the sense that the person behind that account is someone other than who they are claiming to be - whether that is a specific human being with a name and a picture, or just an anonymous, discrete individual who is distinct from anyone else already involved in the conversation.