Actually isitdown shows it to be still online but the website is unavailable.
What I found so far is, YTS.to which is a streaming torrent has shut down.
Popcorntime management team seems to have had an argument about money and power within the team and some members left and the starting group was disbanded. Some members still say they will continue the project though.
David Lemarier has stopped supporting the project, he was one of the leading developers. The facebook account has disappeared also. To make the story short:
Torrentfreak has announced that the developer of popcorntime has shutdown all the servers and there is nothing he can do about it, he also deleted some logs that may have hurt developers working on this.
This decision actually came because there's been attacks on their DNS and some modifications that made it difficult for the remaining team to move all the files. The host (Gandi) didn't comply to help move the files. They also added that so far only Project butter will remain open as it is currently legal but not as friendly as Popcorn was.
https://butterproject.github.io/