Sierra, a 15-year-old student at Sobrante High School, disappeared on March 16 and authorities believe she was murdered, even though her body hasn't been found.
Antolin Garcia-Torres, a 21-year-old Morgan Hill man, is charged with murdering Sierra as well as a special circumstance allegation that he murdered her during a kidnapping. He's scheduled to return to court on Tuesday.
However, Sierra's family still hopes that she can be found alive and volunteers are continuing to conduct searches for her every Wednesday and Saturday, including today.
The car wash is being held at the Sierra Search Center at Burnett Elementary School at 85 Tilton Avenue in Morgan Hill. It began at 10 a.m. and will continue until 2 p.m.
Volunteer Tammy Daly said the car wash is a way for young teens to get involved in the search for Sierra, as people under the age of 18 aren't allowed to participate in the searches.