SAN FRANCISCO -- The San Francisco Police Department is searching for a missing man who requires medication for an ongoing medical condition.

Jerry Tang, 39, of San Francisco was last seen at 8 a.m. Tuesday when his wife, Joyce Tang, left the couple's Upper Haight residence to go to work.

Tang had been feeling ill and was not planning to go into his job as chief technology officer for the startup company Smalltown, according to San Francisco police Inspector Angela Martin.

Joyce Tang spoke with Jerry Tang by telephone at 10 a.m. Tuesday, Martin said. That was the last anybody he knew heard from him.

Tang had a stroke when he was 37, which left some lingering problems with his balance and memory, according to his older brother, Austin Tang. Since his stroke, he has suffered two major seizures. He is supposed to take anti-seizure medication every 12 hours.

"He really keeps a strong face," Austin Tang said. "He's always been the dependable person for his family, but that created a lot of uncertainties for him in life."

Jerry Tang had apparently been under considerable stress recently, dealing with such challenges as helping to get a startup company off the ground, raising his 7- and 4-year-old children and tending to his own health.

Austin Tang said that it was unlike Jerry to show that stress was affecting him, but that recently signs of stress had been visible.

"He's never done anything like this," said Ingrid Overgard, a close family friend. "This is so far out of the range of behavior that anyone here would expect from Jerry. We know he left here on foot with his keys, his wallet and a jacket, but that's all we know."

Martin said that an unconfirmed report from a citizen placed Tang at the corner of Haight and Shrader streets on Tuesday night. A Golden Gate Park groundskeeper reportedly saw him Wednesday night near McLaren Lodge in Golden Gate Park.

"He saw him just sitting in the rain and gave him an umbrella," said Austin Tang, "But when we went back there, he was gone."

Tang was last seen wearing a blue, windbreaker-style jacket, blue jeans and brown shoes, according to Overgard. He is Asian, stands 6 feet 1 inch tall and weighs approximately 160 pounds. He has black hair.

Anyone who has seen or had contact with Tang is encouraged to call the San Francisco Police Department's Missing Persons detail at (415) 558-5508 or (415) 553-1071.