Nothing new was discovered during Saturday's search, which centered in a remote area of San Jose northwest of Morgan Hill.
Search organizer Brian Miller said volunteer turnout was strong despite the weather.
"Today was a rainy day but we were still very happy with today. We had almost 500 new first-time searchers today and we had almost 600 total searchers today."
To have so many people show up on a rainy mornings is a good sign, Miller said.
"I think that puts us in a good position moving forward," he said.
Santa Clara County Sheriff's deputies used off-road vehicles Saturday to comb areas in the West Hills, including the South Coyote Creek Trail.
Search efforts have been expanding around the area where Sierra disappeared on her way to school on March 16.
Items belonging to Sierra have been found, including a cell phone, purse and some clothing. On Thursday, one volunteer found a box that said "Stainless Steel Handcuffs" on the side and contained used condoms.
The items were found less than two miles from where Sierra disappeared. The sheriff's office called the items "suspicious" and will test them. Whether they have anything to do with her disappearance or not remains to be seen and won't be known for at least a few weeks.
Searchers will be out again Sunday rain or shine. On Sunday the search will be expanded to around 15 miles around the area where Sierra disappeared.
For those interested in participating in the search, the headquarters is the old Burnett Elementary School in Morgan Hill. The first shifts of searchers begin going out at 8 a.m., but volunteers can arrive later than that.