San Marino High School student Mira Hu was dropped off by her parents at Arcadia High School at 7:30 a.m. Saturday, but the girl failed to show up when her folks arrived to pick her up, according to Arcadia police.
"A short time later she sent a message to her brother indicating that she was running away because she was overwhelmed by school and this exam,'' according to a police statement.
Police do not suspect foul play.
"It's a straight runaway (case) at this time,'' an Arcadia police watch commander told City News Service Sunday.
Hu may be traveling to central or northern California, police said.
She is described as Asian, 5 feet 3 inches tall, 95 pounds with black hair and brown eyes. She was wearing a black jacket, black jeans and was carrying a large navy-colored backpack when she was dropped off at the school.
Anyone with information regarding Mira's whereabouts was urged to call Arcadia police at (626) 574-5121 or the local law enforcement agency in their jurisdiction. Anonymous tips can be provided by calling Crime Stoppers at (800) 222-TIPS.