Police will alert the public when volunteers are needed again.
David Puckett disappeared around 5:30 p.m. Police say he voluntarily left and don't believe any foul play is involved.
By Saturday night, the search had grown to include help from the Denver Police Department's helicopter and a bloodhound from the Jefferson County Sheriff's Office.
More than 150 volunteers joined the search Sunday.
"I'm anxious with how cold it is that something might really bad happen to him", said David's mom, Stephanie Puckett. "And if you guys can, please help me find him".
He was last seen wearing green camouflage trousers, a black T-shirt, orange boots and a tan girl's coat, according to police.
The AMBER Alert describes David as a white male with brown hair and hazel eyes. He has a minor learning disability. He has a history of wandering, according to police. Police mentioned two other occasions where David was found by neighbors. Police said other parents might not be aware that David has been reported missing. They are asking residents to check their property.
'We will make these efforts to speak with you'. Here's a drone taking off in hopes of #FindingDavid.
"We are continuing to do thorough searches of the neighborhoods, canvas searches, and also some interviews", McCoy said.
McCoy said the Colorado Bureau of Investigation is set to issue an Amber Alert in the case, something that was delayed in part because there was no immediate evidence that there was an abduction. Police don't believe the cases are connected. If you see him, please call the police immediately.