Hi Tim,
Instead of this:
sym.getComposition().getStage().getSymbol("allButtons").getSymbol("Button" +buttonClicked).stop("Touch");
Try this:
sym.getParentSymbol().getSymbol("Button" +buttonClicked).stop("Touch");
Or even easier (if your button will always be in the symbol that you want to control):
sym.stop("Touch")
For more info:
Adobe Edge Animate CC JavaScript API
hth,
Joe