Sierra, 15, disappeared after she left for school on the morning of March 16, prompting extensive searches of the area. Sheriff's investigators have said they believe her disappearance is an abduction.
"This is not how I wanted to acknowledge this date, but I am deeply grateful that the community continues to support her cause," Sierra's father, Steve LaMar said in a statement Tuesday.
The KlaasKids Foundation, an organization that provides search-and-rescue services for families of missing people, are organizing today's search as well as a search on Saturday.
Volunteers are asked to report to the Find Sierra Search Center at Burnett Elementary School, located at 85 Tilton Road in Morgan Hill, between 8 a.m. and 1 p.m.
Volunteers must be at least 18 years old and photo ID is required, organizers said.
Organizers said the searches will take place in various terrains, including dense woods, and volunteers are urged to bring water, snacks, bug spray, gloves and a hiking stick.
Anyone with information is asked to contact sheriff's investigators at (408) 808-4500 or call the anonymous tip line at (408) 808-4431.