A Silver Alert has been issued for a missing 81-year-old man who was last seen in West Greenwich, according to the Rhode Island State Police.Frank Bergheimer, who has dementia, was last seen at 9 a.m. Wednesday at a park-and-ride on New London Turnpike in West Greenwich, where his vehicle was left unattended, according to the state police.His is 5 feet, 9 inches, 163 pounds, wears glasses and has a goatee.