The robbery was reported at about 9:20 p.m. near Mission and Seventh streets.
The 46-year-old victim had parked his truck outside the store and gone inside, and when he returned, he saw the three teens jumping on the vehicle's bumper, according to police.
When the man ordered them to get off, one of the teens sprayed him with pepper spray, then went into the cab of the truck and took the man's laptop and backpack, police said.
The teens then fled and hadn't been found as of this morning.
Anyone with information about the case is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.