The posters include Sierra's name, photo and description as well as law enforcement contact information. Transit riders with smart phones will be able to scan a QR code on the posters to obtain additional information.
Sierra, 15, disappeared the morning of March 16, when she did not report to school, according to the Santa Clara County Sheriff's Office, which has been conducting extensive searches on land and underwater near Sierra's home, where she was last seen.
The sheriff's office is treating the high school sophomore's disappearance as an abduction.
The KlaasKids Foundation provides search-and-rescue services for families of missing people.
