The search for missing Morgan Hill teenager Sierra LaMar drew its most famous volunteer to date when San Francisco 49ers quarterback Alex Smith joined the effort Saturday.

Marc Klaas, whose daughter Polly was killed in 1993 after being kidnapped from her Petaluma home, confirmed that Smith was among 581 people who turned out to search for the 15-year-old girl missing for two weeks.

“He wasn’t there for attention. He was there to search,” said 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 added that this was the first time he could recall that a celebrity came forward without prompting. “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’s presence was trumpeted on Twitter, but his team made no mention of his efforts. Attempts to reach Smith were unsuccessful, and a message left for 49ers’ public-relations staff was not returned.

The quarterback is coming off the best of his seven seasons with the 49ers, leading them to the NFC Championship Game. He and his family live in Los Gatos.

The No. 1 overall pick in the 2005 draft, Smith established the Alex Smith Foundation for foster teens a year later. He signed a three-year contract on March 21 to remain with the 49ers rather than enter the free-agent market.

The Twittersphere offered praise for the quarterback. One tweet said: “S/O to Alex Smith for helping the search team find Sierra Lamar. #Respect”

Smith also dropped off food and water before joining the search, which stretched through the fields, hills and neighborhoods within a 20-mile radius of Sierra’s home, where she was last seen on March 16.

The teen had left for school that morning but never showed up for classes.

Staff writer Chris De Benedetti contributed to this report.