Yalani Chinyamurindi, 19, was killed Jan. 9 while sitting in a stolen car on Page Street with three other African-American men in their early 20s.
Police say three of the victims had gang ties and guns were found inside the car.
Chinyamurindi's funeral was Saturday. His mother, Asale-Hasqueenyah Chandler, says she's set up a trust fund to help find those responsible for her son's death.
"We want multiple private investigators to go in to put fear in them young people to let them know that you cannot keep it a secret and you cannot go and start executing anyone, let alone four at a time," she said.
Police have not made any arrests in the case. They say they are stepping up patrols to head off any more violence.
Anyone with information on the homicide is asked to call San Francisco police at (415) 575-4444 or send a tip by text message to TIP411 with "SFPD" at the start of the message.