"It looks like the other victim may be involved," police spokeswoman Margo Rohrbacher said late this morning.
Authorities had been searching for the woman by air in the China Camp area, Rohrbacher said.
Police said earlier this morning that two women were waiting at a bus stop in the 200 block of Canal Street when a woman pulled up to them in a black sport utility vehicle and offered them a ride.
The women, who did not know each other, both accepted the ride and got into the SUV, police said. The woman behind the wheel then drove them a couple of blocks to a Burger King restaurant on East Francisco Boulevard, where she stopped and two men wearing ski masks got into the car.
One was armed with a knife and the other with a handgun, Rohrbacher said.
The men robbed the women and then the group drove to northern San Rafael and into Santa Venetia, where they drove around for a short period before letting one of the victims out of the car, Rohrbacher said.
The woman who was released flagged down another motorist and got a ride to Corte Madera, where she reported the incident to police.
Police kicked off a search for the second woman from the bus stop but called it off after they came to believe that woman may have been in on the kidnapping.
She is described as a Hispanic female in her 40s with black hair in a bun and a brown sweater. She was short and heavyset.
The suspects' vehicle was described as a black SUV, possibly a Chevrolet. It was a model 2000 or newer and had black tinted rear windows and a silver license plate frame.
The driver of the SUV was described as a Hispanic female about 35 years old with brown hair to the middle of her back. She was wearing a black sweater, black pants and eyeglasses.
Another suspect was described as a young Hispanic male, possibly about 17 years old, wearing a black hoodie with the hood up and black pants. He was short and heavyset with light skin and armed with a knife.
The last suspect was described as a Hispanic man about 27 years old or older with dark skin and a thin build. He was about 5 feet 8 inches to 5 feet 9 inches tall and wore a black sweater, black pants and carried a black handgun.
Both the males were wearing ski masks.
Anyone with information about suspects or the victim is asked to call San Rafael police at (415) 485-3000 or contact their local law enforcement agency.