According to police spokesman Officer Albie Esparza, the victim came at about 8:30 p.m. to a woman's apartment in the Alemany housing development, located in the 500 block of Alemany Boulevard.
The woman walked to the back of the apartment, heard a gunshot, and came back to find the victim shot in the head near the front door, Esparza said. He was pronounced dead at the scene.
The victim was identified today by the medical examiner's office as 18-year-old Calin Hunter.
Esparza said an unknown suspect is believed to have come to the front door and shot Hunter there. No arrests have been made. Information on Hunter's relationship to the woman is still being investigated, according to Esparza.
Anyone with information about the case is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a text message to TIP411.
The shooting is San Francisco's 47th homicide this year.