ActionScript 3.0 :: How To Retrieve Named Object

Inside my loop, where i get my XML objects I added a code to draw and add the mask:
 
var myMask:MovieClip = new MovieClip();
// settings for width height x y color fill etc etc.
myMask.name = "NAME-"+i; // set the NAME
myContainer.addChild(myMask);
myContainer.mask = myMask;

 the mask looks fine on the stage.now since i name it, i want to use it for other purpose like moving it now i want to actual call myMask
i get my number "num" from other function, that works fine
 
function applyMask(num:int):void {
// need to call   myMask("NAME-"+num)
}
 
i have tried myContainer.getChildByNamehave tried:         

var masking:myContainer=getChildByName("NAME-"+String(num)) as myContainer;

i have traced for options i can think of myself, but all result no property found.