Sierra, 15, has been missing since March and is presumed dead.
Detectives are investigating the body discovered Friday as a homicide, according to KTVU TV.
Original story, 4 p.m. Friday: A dead body was found in a rural area close to the intersection of highways 101 and 156 in Aromas on Friday, local media is reporting.
Pedestrians made the grisly discovery on Cannon Road around 9:20 a.m., according to KSBW Action News 8.
Investigators have yet to release the gender, age or name of the person, the Santa Cruz Sentinel reported. It was found about 100 feet off the road.
Cannon Road is closed between Highway 101 and Brown Road while investigators work, according to the Sentinel.
The probe is being led by the San Benito County Sheriff's Office with assistance from the Santa Clara County Sheriff's Office.