"I just see, like, everybody going crazy and messing with her, and I was like, 'Hey man, calm down, leave her alone, that's a little girl.' You don't do nothing like that, because I got two 15-year-old sisters myself," Rodriquez said.
He said he knew at least one of the attackers and tried to stop the group from taking pictures of the victim on their cell phones.
Rodriguez told KGO he was the only person who tried to help the victim, who was lying naked alone by the time the attack ended.
"She was by herself, she was naked and I tried to help her and I reached for her and she started screaming and I said, 'Hey, I don't want to hurt you, I just want to help, that's all I want to do is just help you,'" Rodriguez said. "So she stopped screaming. It's as if she knew, you know, I wasn't trying to do nothing and then I grabbed my T-shirt and covered her up with it."
Fearful of being labeled a snitch -- a reputation that Rodriguez said could put his life in danger -- the teen said he was too scared to call for help.
"People say, 'Why didn't I call the cops,' but at the same time, I live in Richmond. A neighborhood like this, snitching is something you don't do, you know. I mean I have to walk down the streets now in fear of my life," Rodriquez said.
Someone who heard people talking about the attack eventually called the cops.
"We didn't want to go back there because we were scared," Margarita Vargas told the police dispatcher. "Nobody wants to call the cops, so we decided to call the cops."
The victim is described by friends as a devout Christian who attended church three times a week; her friends said she had been looking forward to the homecoming dance for weeks.
The Associated Press contributed to this report.