MMO plugin? There is no such thing. You can't simply put MMO features into one plugin.
There is that online chat plugin - sort of. You can also pass and receive data to the server with AJAX plugin. That's all the functionality you need to establish a server-client architecture.
Now, server is a wholly different can of worms. Can't make those in Construct 2, because C2 is oriented to browser game development. No, you need to create a program running on the server that would handle clients and run the game. Which means programming.
All in all, this is an unrealistic request.