The kidnapping was reported at 3:42 p.m. Tuesday at the intersection of Mission and 10th streets.
The 20-year-old victim and another person were walking when the suspect drove up behind them, pulled the victim into his vehicle and drove away west on Mission Street, police said.
Police spokesman Sgt. Daryl Fong said police are treating the case as an isolated incident and said "it doesn't appear to be a public safety issue."
Fong said the suspect and victim "have some sort of relationship" and that the victim was still missing as of Wednesday morning.
No other details about the case were being released, he said.
Anyone with information about the kidnapping is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.