Smith and 580 other volunteers searched for the 15-year-old, who disappeared March 16 while on her way to school in Morgan Hill, a city located southeast of San Jose.
"He wasn't there for attention. He was there to search," said Marc Klaas, founder of the KlaasKids Foundation. "It was about his heart. It's certainly a touching thing, and it's a huge thing, too. By showing up, he provided a value that went well beyond his own presence as a searcher."
Klaas confirmed that Smith was part of the search. Smith brought food and water, then helped look through the fields, hills and neighborhoods that are within a 20-mile radius of the teen's home.
"For somebody of that stature to take his own initiative and do something like this, to show that he cares about the family and the community, I'm just thrilled, and I imagine Sierra LaMar's family is, too," Klaas said. "It shows you the kind of person Alex Smith must be."
Smith recently agreed to return to the 49ers rather than sign with another team as a free agent. The quarterback threw for 3,144 yards and 17 touchdowns while leading the team to the NFC Championship Game.