Mark (Markiplier) and Dan (NerdCubed) have indeed helped, as have Ze, Diction, Chilled, Rachel, etc.

The problem with having PewDiePie play it, is that yes it would get a load of new players, but it would be as other people have said, 'introducing a load of under-aged players' to the game and I don't know if we would survive so many players that have no idea what they are doing with anything.