The following text has been taken verbatim from The SMFTA

SFMTA is responsible for removing illegally parked and abandoned vehicles from city streets. The SFMTA conducts tows requested by Enforcement and the San Francisco Police Department (SFPD). A vehicle which is parked in a tow away zone will be towed to one of the City and County of San Francisco Impound facilities.

Towing helps maximize on-street parking, manage traffic congestion, and maintain clean, safe and functional streets for the public’s use. Most tow requests received from the public are for blocked driveways. Request Enforcement or call 311 to report an illegally parked vehicle.

If you think your car is towed, immediately call City and County of San Francisco Impound at 415.865.8200. The City’s contractor, AutoReturn, will help you search for your vehicle. Be ready to provide your license plate number, vehicle description, suspected tow date, and location.

If we cannot confirm your vehicle is towed, your vehicle may be stolen. To report a vehicle stolen, go to the San Francisco Police Department (SFPD) or call 415.553.0123.

So the best people to speak to if your car has been towed are the SFPD.