On Thursday, a National Guard helicopter and searchers on horses joined about 125 volunteers searching through rain-soaked brush and steep terrain around the Skyline Elementary School in Portland.
The boy's father appealed to the community for help in finding the boy.
"We as family know how difficult and stressful this is, but memories and statements can help find Kyron," Kaine Horman said at a news conference.
"Please help us bring Kyron home," he said.
Local, state and federal authorities have combed the area near the school. By the beginning of the week, more than two-thirds of the school's students, about 300 children in grades K-8, volunteered to be interviewed by police.
The strain of the search was evident on the faces of Kyron's parents and stepparents, all of whom attended today's press conference wearing matching "Missing" T-shirts with pictures of Kyron's face on them.
"One little boy's smile can impact a community," Kyron's stepfather said.
Police on Wednesday said they had received more than 1,200 tips, mostly from Oregon and Washington state.
"We are looking for a living Kyron Horman," said Multnomah County Sheriff's Capt. Jason Gates at the time.
Gina Zimmerman, president of the school PTA, told the Portland Oregonian this week that her 8-year-old daughter Madi has been a classmate of Kyron's for three years.
"He's not the type of child who would just go out of school and go searching or wandering around," Zimmerman said. "He's just a timid, sweet boy.
"Everybody's just worried and in shock that this could happen in our little school where everybody knows everybody," she said.