It sure looks like the droppings of Tomato Hornworms. You could try the soapy water method to get the worms to show themselves:
http://www.veggiegardener.com/... and then you can pick them off and drown or squish them; or you might also want to consider an organic method of eradication like using a mixture of water, insecticidal soap and crushed or powdered hot cayenne pepper.