The incident happened in Lake Elsinore near Summerhill Drive and Railroad Canyon Road on Friday at about 5 a.m.
The suspect is described as a 20-to 21-year-old black man, between 5 feet 5 inches and 5 feet 6 inches tall, weighing about 160 pounds.
Officials said the suspect sexually battered the girl while she walked to a bus stop and waited for the bus to arrive.
Authorities said the suspect was wearing a red hat with white letters, a black shirt, blue jeans and carrying a red backpack.
If you have any information regarding this investigation, you're urged to call the Lake Elsinore Police Department at (951) 245-3300.