Police said the child was last seen April 17 around 9 p.m. in the 100 block of Dole Avenue.
They told police they discovered him missing when they woke up Thursday morning.
He has short, blonde hair, and weighs about 70 pounds.
He was last seen wearing a blue sweatshirt with Mario Brothers on the front and black sweatpants.
Police used dogs to search his parents’ car, and bloodhounds to track his scent. Officers also searched nearby trash cans, and spoke with neighbors.
Firefighters and members of the dive team also searched parts of Crystal Lake.
The FBI also has joined the search effort.
Anyone with information is asked to call police at 815-356-3620.
According to police, an Amber alert was not issued in this case due to law enforcement being unable to confirm an abduction occurred.
The boys parents were not at the house for much of the day. Neighbors said they left with police this morning.