click or touch event for Box Collider 2D

I have a Box Collider 2D and need to know when the user clicks or touches (for touch screen) the object. I tried adding OnMouseDown but this doesn't always seem to get triggered.
I also tried to use the Raycast but that doesn't seem to always work either.

I haven't found anything that seems consistent yet.

Here's what I tried for touch:
if (Input.GetMouseButtonDown (0)) {
Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);

RaycastHit hit;
// Casts the ray and get the first game object hit
if (Physics.Raycast (ray, out hit))
OnMouseClick ();
//Debug.Log(hit.transform.gameObject);
}

if (Input.touchCount == 1)
{
Vector3 wp = Camera.main.ScreenToWorldPoint(Input.GetTouch(0).position);
Vector2 touchPos = new Vector2(wp.x, wp.y);
if (collider2D == Physics2D.OverlapPoint(touchPos))
{
OnMouseClick();

}
}

Thanks.

 

http://forum.unity3d.com/threads/233483-Touching-a-2d-sprite

 

thank you
jbassking