The attack occurred on Oct. 28 after one of the suspects made contact with the victim via www.myredbook.com, an online website for escorts and masseuses, police Inspector Vince Repetto said.
He did not disclose the exact location of the motel, citing the ongoing investigation.
The suspect showed up and paid for sex in the motel room, then called his friend, who also came and paid for sex while he waited outside, Repetto said.
The two men then left the motel but surveillance video showed that they hung around in the area for several hours before the first suspect returned and robbed and raped the victim at gunpoint, Repetto said.
He said the suspects likely waited, "assuming she was going to have more customers and more cash."
Repetto said the pair likely worked as a team and "may have victimized other women that utilize these websites."
Investigators haven't gotten any other similar reports recently, but "a lot of the time, these victims are hesitant to come to police," Repetto said.
Sketches have been released of the two suspects. The one who sexually assaulted the woman is described as a possibly half-black, half-Hispanic man who is between 25 and 30 years old, about 5 feet 9 inches tall and weighs about 160 pounds, police said.
The other suspect wore a black San Francisco Giants hat, but a detailed description of him was not available, Repetto said.
Anyone with information about the case is encouraged to call Repetto in the Police Department's special victims unit at (415) 553-9117.