I guess not, considering that Stencyl Programs don't outsource to other programs, unless you specifically upload a file. I'm assuming in order to create a multiplayer game, that you need to create a program that outsources to the internet.
On the other hand it could be really simple. You could make a game that is multiplayer, but the multiple players would have to share the same computer. Let's say you wanted to race two characters, with two players sharing the computer. You could have First Player's Actor Type follow the mouse, while Second Player's Actor Type is controlled by W,A,S,D or Arrow Keys.
^That's the only way I can think it would work^