It happened on Aug. 28 just after 9:30 a.m. on Parker Avenue near Ney Avenue.
Police say the victim was walking down the street when the man, armed with a gun, approached from behind and tackled the victim to the ground and began sexually assaulting them.
The victim screamed for help and the man ran away, but stole the victim's cell phone.
If you know anything about this case, police urgently ask you to contact the OPD Special Victims Unit at (510) 238-3641 or the TIP LINE at (510) 238-7950.