LA VISTA, Neb. (AP) — Authorities have continued to search this weekend for an autistic 11-year-old boy who has been missing since he walked out of his elementary school last Monday.

La Vista Police focused their search for Ryan Larsen Saturday on Walnut Creek Recreation Area, which is a large park with a lake, wooded areas and miles of trails. Police used K-9 teams and a State Patrol helicopter assisted from the air.

In addition to the local search effort, police said details about Larsen’s disappearance have also been posted on the National Center for Missing and Exploited Children’s website.

Larsen has been missing since he walked out of his elementary school Monday during changes in morning classed in La Vista, which lies just southwest of Omaha. He has been without medication he takes for seizures since he disappeared.

Police have said the child has a history of hiding from his family and authorities. La Vista Police Chief Bob Lausten has said his department has had to find the boy at least half-a-dozen times, but that he’s never been missing for days at a time.

Investigators said the family’s computer showed a recent history of online searches using the phrases “hiding from the police,” “hiding underground,” and “how to avoid being spotted.”