The four-year-old girl, known only as Maria, was thought to have been abducted. She was found in squalid conditions with a couple and 13 other children at a camp near Farsala.
Kerry Needham, whose son was just 21 months old when he vanished on the island of Kos in 1991, said: "We have always believed Ben's abduction was gypsy-related and have had a long ongoing inquiry in Larissa.
"We hope the investigation into Ben's disappearance will now be looked at again."
The Sheffield youngster vanished after travelling to Kos with his mother and grandparents Eddie and Christine, who were renovating a farmhouse in the village of Iraklise.
Maria was found after a police officer attending the camp noticed she bore no likeness to her supposed family and investigated further.
The discovery has also buoyed the hopes of Madeleine McCann's parents. A spokesman for Kate and Gerry McCann said Maria had renewed their hope Madeleine would be found. She went missing in Praia da Luz, Portugal, on May 3, 2007.