Investigators say the suspect arranged to meet the girl at South Coast Plaza in Costa Mesa after swapping notes with her on the MySpace social networking Web site.
Police say the two went to a motel, Zaby's Motor Lodge at Harbor Blvd. and Katella Avenue, where they had sex.
Investigators say the suspect took the young girl's bus pass and left her stranded.
A short time later she flagged down a civilian police traffic controller and told him she wanted to go home.
Police say the young girl did not initially reveal the sexual assault.
That revelation came later when it was revealed the girl was the subject of a missing persons report.
Police say they believe Casteneda may have victimized other minors.
Anyone with information is asked to contact the Anaheim Police Department at (714) 765-1958.
City News Service and the Associated Press contributed to this report.