Movie clip over button

Question

I have a mc over each of my buttons to play when the button is clicked.  The mc's instance name is the same as the button's instance name but with "_mc" added.  I cant seem to get this part to work:
var btn_mc:MovieClip=this(instanceName+"_mc");
here is the full code ...
function addPListeners():void {
     for (var j:uint = 0; j < PButtons.length; j++) {
          PButtons[j].addEventListener(MouseEvent.CLICK, goSection);
addPListeners();
function goSection(event:Event):void {
     var instanceName:String=event.target.name;
     var btn_mc:MovieClip=this(instanceName+"_mc");
     TweenLite.to(btn_mc, 1, {autoAlpha:0});
     trace(btn_mc);

Answer 1

with some assumptions about your code you didn't clarify and isn't apparent, you would use:
function addPListeners():void {
     for (var j:uint = 0; j < PButtons.length; j++) {
          PButtons[j].addEventListener(MouseEvent.CLICK, goSection);
addPListeners();
function goSection(event:Event):void {
     var instanceName:String=event.target.name;
    var btn_mc:MovieClip=MovieClip(this[instanceName+"_mc"]);
     TweenLite.to(btn_mc, 1, {autoAlpha:0});
     trace(btn_mc);