2d - Follow cursor by having object rotate around z-axis

Using the overhead view how can I move the mouse cursor around the screen while having the object rotate around the z-axis so the object faces the mouse cursor. I thought something like the code below would work but apparently not. transform.LookAt (new Vector3 (Input.mousePosition.x, Input.mousePosition.y, 0)); I know very little so if you could explain your code that would be very helpful. Thanks!