Triggering a subclip

On a frame of a canvas timeline I have a movie clip with a subclip animation. It plays fine within the subclip. I am attempting to initiate that animation with a mouse click, but nothing happens. The symbol instance is "pizza" and the button instance is "pizzago." Below is my code. The script is on the same frame as the movieclip I'm trying to play. 

var _this = this;
_this.pizzago.on('click', function(){
_this.pizza.play();
});