US authorities have rejected a teenager's claim that he is an Illinois boy who disappeared eight years ago.

A 14-year-old boy told police he had escaped from kidnappers and claimed to be Timmothy Pitzen, who vanished in 2011 at the age of six after his mother's suicide in a motel in Rockford.

The teenager claiming to be Timmothy said that after escaping his kidnappers this week "he kept running across a bridge" into Kentucky.

He was found walking alone in Newport, Kentucky, early on Wednesday morning - around 800km from where Timmothy went missing.

But the Associated Press has said the boy claiming to be Timmothy is not.

It has quoted the FBI as saying DNA testing ruled out the teenager as being the missing boy.

Authorities did not immediately release the teenager's true identity or other information.

A Joliet Police K9 officer searches Castle Rock State Park wetlands for evidence on Timmothy Pitzen's disappearance, 19-05-2011. Image: Heather Charles/Chicago Tribune/TNS/Sipa USA

Investigation

The boy told officers that he had been kept at a Red Roof Inn by two men, although there are a number of motels with that name in area and it is unclear which one he was referring to.

Police forces in the area were investigating hotels with the same name near to them.

The teenager claimed the two men drove a Ford SUV with Wisconsin number plates.

He was taken to hospital for DNA tests to confirm his identity.

Age progression photo of Timmothy Pitzen released on the US National Missing and Unidentified Persons System, 11-02-2015.

Missing

Timmothy Pitzen was dropped off at school in Aurora, Illinois, on May 11th 2011 by his father - but was picked up just hours later by his mother, Amy Fry-Pitzen, who took him on a trip.

They drove to Wisconsin and visited the zoo and a water park together - the last place that Timmothy was seen alive.

Two days later, his mother was found dead in a motel room.

Reports at the time said that she checked in alone and had written a cryptic note that said her son was safe, but adding: "You'll never find him."

Pitzen was never seen again.

Alana Anderson, mother of Amy Fry-Pitzen and grandmother of Timmothy Pitzen, 16-11-2011. Image: Stacey Wescott/Chicago Tribune/TNS/Sipa

“False hopes”

Speaking earlier to local TV channel WISN-TV in Wisconsin, Pitzen's grandmother said: "We just know a 14-year-old boy was found and went to the police.

"We don't want to get our hopes up and our family's hopes up until we know something.

"We just don't want to get our hopes up. We've had false reports and false hopes before."