Keu Thang, 89, has been missing since about 7 p.m., authorities said.
Thang, who suffers from medical and mental disabilities that require medical attention, takes medication for high blood pressure and may be in the early stages of dementia, police officials said.
Police said she often hangs out near Pier 39 and the Financial District.
Officials describe Thang as an Asian woman, standing 5 feet 2 inches tall, with brown eyes and gray hair. She was last seen wearing a burgundy overcoat with a black hood and possibly a green fanny pack.
Anyone with information about Thang or her whereabouts are asked to call San Francisco police at (415) 575-4444 or text a tip to TIP411.
Rachel Purdy, Bay City News