They said Charles Mouat walked away from his house in the 100 block of Caswell Avenue in the Collegeville section of Lower Providence Township around 4:00 Thursday afternoon.
Officers said Mouat, 68, has dementia and other health issues and takes several prescription medications that he did not take with him.
Mouat, who stands 5 feet, 11 inches and weighs 150 pounds, was last seen wearing a gray T-shirt, blue jeans and black shoes.
Police said he doesn't have any ID with him.
Anyone with information is asked to contact the Lower Providence Township Police Department at 610-539-5900.
Police say a day-long search on Friday, which included a State Police helicopter and a dive team, has not been successful in locating Mouat.