Robert Davis, 93, was last seen on Feb. 26 as he left Marin Joe's restaurant in Corte Madera.
The World War II veteran was supposed to drive straight home following a weekly dinner with his daughter, but he never made it.
San Rafael police did a helicopter search for Davis on Friday, but found no signs of him or his car.
Davis was driving a 2001 silver Toyota Camry with California license plate number 4SEY056. The car is missing a right front hubcap and may have damage to one of the fenders.
Police said Davis suffers from a medical condition and may have become disoriented. It was raining heavily when he left so he may have gotten lost on his way home.
Davis is a white man with gray hair and gray eyes who stands 5 feet 7 inches tall and weighs 139 pounds. He was wearing a beige jacket, yellow sweater and beige slacks when he was last seen
Anyone who has seen him is asked to call San Rafael police at (415) 485-3000 or 911.
(ABC7 News reporter Lisa Amin Gulezian and Bay City News contributed to this report)