The suspect is 25-year-old Damir Shalako who has distinctive tattoos on his neck.
Police say the attack happened at noon on Tuesday in the Potrero Hill housing development, where the suspect lives with his grandmother.
"He subsequently entered another resident's location next door, sexually assaulted a female about 45 years of age, robbed her, took about $1,000 cash and beat her severely," said San Francisco Assistant Police Chief Jeff Godown.
Police say the grandmother heard the woman's screams and went next door. She tried to stop her grandson, but he ran.
Police do not know if he's armed. They say if you see him, do not approach him, call 911.