Mira Hu, 16, was last seen on Saturday after she walked out of her SAT exams at Arcadia High School.
Authorities said she sent a text message to her brother saying she was stressed about school.
She was believed to be on her way to Central or Northern California.
San Marino police did not indicate where she was found but said the teen is back with her family.
Mira Hu has been found, is safe with her parents and San Marino PD @SanMarinoPD Thank you to all who assisted in her return— SanMarinoPDCOP (@SanMarinoPDCOP) June 9, 2015