The 15-year-old girl, Kristina Krag, left her Glenmoor neighborhood home at 4 p.m. Thursday and has not been seen since, Fremont police said.
She is described as a white female standing 5 feet 4 inches tall and weighing 160 pounds. She has brown hair that was in a ponytail.
She was last seen wearing a pink T-shirt, jeans and black tennis shoes, police said.
The missing girl is a special needs student, police said.
Anyone with information about her whereabouts is asked to call the Fremont Police Department at (510) 790-6800.