Problem with triggers

//This is my object drag, might help.. it's a .cs code attached to the game object
    void OnMouseDrag()
    {
        Vector3 curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
        Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;
        if (Global.noGrid[0]) //noGrid means inside the grid ('no' in Portuguese means 'in')
        {
            transform.position = Global.FindClosestObject(curPosition, "gizmo_peca").transform.position; // here i find the game closest gameobject inside the grid, i do that because i need a snap (that's why i need the trigger working to, to recognize which gameobject it's colliding
        }
        else
        {
            transform.position = new Vector3(curPosition.x, curPosition.y, curPosition.z);
        }

    }

// This is what i tried but with no success in BlockForma.cs (It's how I call my gameobject above)
    void OnTriggerEnter2D(Collider2D c)
    {

        if (c.tag == "Forma")
        {
            c.rigidbody2D.velocity = new Vector2(0,0);
            Debug.Log("Hello");
        }
    }