The girl was walking home alone following an after-school program when the suspect grabbed her, threw her into a car, drove to a secluded area and sexually assaulted her. He then let her go.
School district officials put out a warning to students and parents after the attack.
"Definitely parents need to be aware that it's not the same world that they grew up in, and so there is a lot more danger than perhaps there was in their childhood. And so children walking home alone is definitely a risk," said Diana Asseier, assistant superintendent of Alvord Unified School District.
"I get a ride from my friend, and when I come to school, I make sure I have people with me, and when I'm walking to school, I also have people with me," said student Audrey Montowine.
Authorities say suspects like this normally don't stop with one attack, and they fear the man will try to strike again. They say often suspects can get increasingly violent with each attack.
Police released a composite sketch of the suspect. He is described as a man in his 20s to mid-30s, with a thin build, blond hair, facial hair and a tattoo on his right forearm. The suspect's vehicle is described as a 1980s four-door Toyota sedan with a faded red paint job and tinted windows.
Anyone with information is urged to call the Riverside Police Department at (951 353-7126.