Maddox Scott Ritch was last seen at Rankin Lake Park in Gastonia, located about 20 miles away from Charlotte.
He had been walking in the park with his father and another adult when he ran up ahead and they couldn’t keep up, according to reports.
The child is described as white, with blond hair and blue eyes. He’s 4 feet tall and weighs about 45 pounds.
He was last seen wearing an orange T-shirt with “I am the man” written on it and black shorts with a white stripe.
Officers are checking surveillance video from nearby houses and businesses, and following up on various tips and interviews, the Gastonia Police Department said. The lake is also being searched.
The FBI’s Charlotte field office has joined the investigation.
"We're going to explore all possibilities, including abduction, but we're also going to make sure we search every inch of land around here to make sure that he's not simply lost," Special Agent Jason Kaplan told reporters Sunday.
Anyone with information is urged to call the Gastonia police tip line at 704-869-1075.