Lawrence police this morning are asking for help in finding a man suspected in two convenience store holdups Monday night.According to a statement released this morning, police are seeking a 20- to 23-year-old “heavy-set” black man, about 6 feet tall, 200 pounds who has a “scraggly goatee.” The man was last seen wearing a gray hooded sweatshirt with several shirts underneath, dark-tinted sunglasses with square-shaped rims and dark-colored long pants.Police said at 8:30 p.m., a staff member at the Speedway Shell, 1733 Mass., reported a man displayed a knife and demanded cash. But the staff member, a 55-year-old Lawrence man, refused and the suspect left and ran away south and west.Also at 9:10 p.m., a 39-year-old Lawrence man working at University Phillips 66, 2434 Iowa, reported a man with a similar description had a knife and demanded cash. The suspect received an undetermined amount of money and ran south.Police are asking anyone with information to call the department at 832-7501.