LA PORTE CITY, Iowa (AP) — Authorities have switched to a surgical approach in their search for a missing 16-year-old boy in eastern Iowa.

Black Hawk County Sheriff Tony Thompson said Wednesday that volunteers are no longer being sought because search operations for Jake Wilson now will be carried out by personnel with specific skills. He says the broad net formed of hundreds of searchers is being followed by "a very surgical approach."

Police say Jake, of La Porte City, was last seen at 9 p.m. Saturday going for a walk. A search began less than an hour later, when he didn't return home. His mother, Megan Neiswonger, has said Jake has autism with a mild intellectual disorder and functions at the level of a 9-year-old.

She told the Waterloo-Cedar Falls Courier that the situation is "running us down."

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Information from: Waterloo-Cedar Falls Courier, http://www.wcfcourier.com