Bernard Nuble was reported missing by a relative on July 5 at 12:10 p.m., according to police.
Authorities said Nuble was last seen around 8:30 a.m. on July 4 in the 2200 block of McClellan Street.
Police describe Nuble as standing about 6 feet, 4 inches tall and weighing approximately 150 pounds.
"He suffers from a diminished mental capacity and may currently be disoriented," police said in a news release. "Nuble has a medical stoma on his throat and utilizes an electronic voice box to communicate."
Investigators said Nuble is known to frequent the areas near 5th and Duncannon streets and 11th Street and Lehigh Avenue.
Anyone with information about Nuble's whereabouts is asked to contact the South Detective Division at 215-686-3013 or call 911.