Police said that Phuong Le, 24, left her Suisun City residence at around 4 p.m. on Sunday without telling family members where she was going.
When the family didn't hear anything from her, Le's brother went looking for her early Monday morning and found Le's car parked at the Barnes and Noble bookstore in Fairfield.
The car was empty besides some of Le's personal belongings and did not appear damaged, police said.
On Tuesday, Fairfield police began working with Suisun City police to locate the missing woman. Police determined that Le regularly visits the Barnes and Noble coffee shop, and found a witness there who had seen her at approximately 8:30 p.m. on Monday.
Volunteers and police have handed out fliers in the area, but police say Le's whereabouts are still unknown.
Police are asking anyone with information about Le's whereabouts to contact Fairfield police at (707) 428-7300 or a tip line specifically for this case at (707) 428-7345.