Barbatis

I think its just a hoax. You can clearly see they already followed stephen king month / years ago. They just clicked unfollow and directly followed him again after that, so it showed up as recently followed. But when you watch the list of people they follow you can see its a while ago.

I dont think the killer will be the demogorgon. Netflix tweeted those 2 emotes. Skull and Rat. That reminds me of the mindflayer. So my guess is Billy will be the killer.