A blonde girl called Maria, aged five or six, was found at a Greek Roma camp last week, and a couple who claimed to be her parents were arrested.
Kerry Needham, whose son Ben was abducted in Kos aged 21 months, said she always believed gypsies took Ben.
She said Greek police must now "investigate the gypsy theory further".
Ms Needham said Maria's case had given her family "fresh hope and maximum publicity", and she remained certain Ben would be found.
She told the BBC Greek authorities had suggested it would be "impossible" to conceal a blonde-haired child in a gypsy encampment, but the case of Maria - who has blonde hair - proved that wrong.
She said the family had repeatedly claimed Ben had been taken by gypsies, but Greek police had always "strongly denied" the possibility.
Ben, from Sheffield, went missing while on a family holiday in Kos.
Ms Needham said she was in contact with South Yorkshire Police, but the force said there appeared to be "no direct correlation" between the cases of her son and Maria.
A spokesman added: "No investigation is currently being carried out by the force in light of this recent case and officers from South Yorkshire Police will only become involved should authorities in Greece require our assistance."
The girl named Maria was found in central Greece when police, who were carrying out a raid looking for drugs and weapons, noticed the lack of resemblance between the child and the couple claiming to be her parents.
Officers checked documents, and DNA tests later revealed Maria was not related to the couple.
A fake birth certificate suggested she was four years old, but the charity now caring for her says medical examinations have revealed she is probably five or six.
A lawyer for the Roma couple has said Maria was given to them, not kidnapped.
Meanwhile, a spokesman for Kate and Gerry McCann, parents of Madeleine McCann, said the case of Maria had given them hope, according to the Daily Mirror.
Madeleine was three years old when she was abducted in Portugal in 2007, and police investigating her disappearance have received more than 2,400 calls since an appeal on the BBC's Crimewatch programme was broadcast last week.
The mother of a British child who went missing in Greece in 1991 has said the case of a girl allegedly abducted by a Roma couple has given her "fresh hope".