WISCONSIN RAPIDS, Wis. -- The search for a missing autistic boy in Wood County is continuing on Monday.

Authorities said that it's unlikely they'll find the 7-year-old Benjamin "Benjy" Heil in a river near where he went missing four days ago.

Nekoosa Fire Chief Ken Hartje said that dog teams have swept through the Wisconsin River area, but they didn't find a trace of Heil's scent.

Heil was last seen on Thursday playing in the basement of his home in Saratoga.

Hundreds of volunteers and rescue personnel joined the search this weekend using horse-mounted trackers, aircraft and boats. They checked a 5-mile radius around the home, WISC-TV reported.

"There's nothing unturned," said volunteer John Jenks. "I mean all the brush, any building, any tree stand. Obviously, this little boy that could climb a tree so you're looking up in the trees."

Divers scoured the river on Sunday but the team isn't expected to return on Monday.

On Sunday, searchers received a possible glimmer of hope. They found an item that might belong to the boy, WISC-TV reported.

Area residents have been asked to repeatedly check their homes, vehicles and anywhere else the child might seek shelter or food. Heil has been known not to respond when his name is called.

It's not the first time the boy disappeared. Several years ago, he wandered about a mile from home and was found in the basement of an elderly man's home. Searchers checked that residence during this search.