Creating a cube as a selection box and detecting all collided objects inside of it.

Just started work on a 2d rts and I implemented a solution for a selection box where I instantiate a 1x1x1 cube at the original mouse click and then scale it in x and z depending on where the mouseUp position occurred.

I have :

 function OnCollisionEnter ( objectCollided : Collision)
 {
     print("Collided");
         var selectedScript : SelectedScript = Camera.mainCamera.GetComponent(SelectedScript);
         if(objectCollided.gameObject.transform.tag != "Untagged")
         {
             Debug.Log(objectCollided);
             selectedScript.AddUnitToSelection(objectCollided.gameObject);
         }
     
 }

attached to the instantiated cube, the goal being that I want to return each game object that is inside the cube. But I'm not getting any results. Any help would be much appreciated.

(I'm not sure if an issue could be because I've scaled the cube?)

Here is a video demonstrating what I'm trying to ask:

http://www.youtube.com/watch?v=BsIb--hMoV0&feature=youtu.be

EDIT: I'm not even getting the print message to show up in the console

 function OnCollisionEnter ( objectCollided : Collision)
     {
         print("Collided");