The 14-year-old, who was covered in bruises, told a passerby that he is the missing boy, who disappeared in May 2011 aged six.
According to Fox Illinois, the DNA test actually found the 'teenager' was a 24-year-old man named Brian from Medina, Ohio.
The Lousiville department of the FBI has released a tweet saying: "FBILouisville, @FBICincinnati, @AuroraPoliceIL, Newport PD, @CincyPD, and HCSO have been conducting a missing person investigation. DNA results have been returned indicating the person in question is not Timmothy Pitzen.
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"A local investigation continues into this person's true identity. To be clear, law enforcement has not and will not forget Timmothy, and we hope to one day reunite him with his family. Unfortunately, that day will not be today.
"APD continues to lead the investigation into the Timmothy's disappearance. The FBI will support this investigation in any way possible. Anyone with genuine information about the case is asked to call the APD at 630-256-5000 or the NCMEC at 1-800-THE-LOST (1-800-843-5678)."
One resident who saw the 14-year-old, told ABC 7: "He looked like he had been beat up, punched in the face a couple of times.
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"You could see the fear on him and how nervous he was and how he kept pacing. He just looked odd."
Pitzen disappeared in May 2011, after his mother Amy Fry-Pitzen killed herself in a motel. When her body was found three days later, the boy was missing and, according to reports at the time, a note left by Fry-Pitzen claimed he was safe and being looked after, but ended, 'you'll never find him'.
On Wednesday, the teen attended a police station, where a report states: "Timmothy described the two kidnappers as two male, whites, body-builder type build.
"One had black curly hair, Mt. Dew shirt and jeans and has a spider web tattoo on his neck. The other was short in stature and had a snake tattoo on his arms."
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Police from Aurora, Illinois, where Timmothy had lived before he disappeared, quickly made attempts to verify the teen's claims - including requesting a DNA test, which has since proved that wrong.
In a statement prior to the test, officers said: "We've probably had thousands of tips of him popping up in different areas. We have no idea what we're driving down there for.
"It could be Pitzen. It could be a hoax."
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While Aurora Police Sgt. Bill Rowley said: "We have no idea if this is Timmothy Pitzen. We don't know if it's a hoax. Obviously, everyone's hopeful, but we have to be super judicious."
Timmothy's grandmother Alana Anderson told WISN-TV: "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've had false reports and false hopes before."
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Speaking to ABC News she added: "I'm cautiously hopeful, very cautiously hopeful. And if it turns out to be him, we'll be thrilled."
Featured Image Credit: Aurora Police DepartmentTopics: News