Get MovieClip properties without instance name

This is a very basic question but I can’t find the answer anywhere. I want to get the properties of a movieclip placed on the stage from it’s class name only (AS2 linkage). Ultimately I want to loop through multiple objects and don’t want to have to give them all instance names.

Example in AS2 if an object with the linkage myMC was on the stage I would simply use:

width = myMC._width;

In AS3 width = myMC.width returns the error: “1120: Access of undefined property myMC.”

I’ve tried using:

var myMC:MovieClip = new myMC;
addChild(myMC);
width = myMC.width;

which works but creates a new instance of myMC when I want to reference the one that’s already on the stage.