Kerry Needham was speaking as a team of 10 South Yorkshire Police officers appealed for help to find the youngster at the farmhouse where he was last seen on the island of Kos in 1991.
They also confirmed a £10,000 reward from the charity Crimestoppers was available to anyone who provides information which leads to the discovery of Ben, even if they live outside the UK.
Ms Needham said she hoped that Greece’s statute of limitation laws would mean that people may come forward now in the knowledge they can no longer be prosecuted for withholding information.
Speaking on the island, Detective Superintendent Matt Fenwick said: “I believe that it’s highly likely somebody living on Kos today, or somebody that has lived on Kos in the past, will have the answer and know what has happened to Ben Needham.
“We want to appeal to those people to come forward and help us find what has happened to Ben.”
Ben, from Sheffield, was 21 months old when he vanished on July 24, 1991, after travelling to the island with his mother and grandparents.
Over the years, there have been a number of possible sightings and a range of theories about what happened to the youngster, who would now be 26.
Earlier this year, South Yorkshire Police announced that they had received extra funding from the Home Office to help in the search.
Ms Needham told the BBC: “We need to look to the future and remain positive and hopefully get some answers.
'He deserves to know the truth and so do we' British detectives make a new appeal for information in Kos, Greece.— BBC Breakfast (@BBCBreakfast) May 10, 2016
“I have every faith in South Yorkshire Police.
“They are amazing detectives. I couldn’t wish for any more from them.
“There’s no words to describe how much this means to me.
“Ben wasn’t abducted by aliens. The ground did not open up and swallow him.
“Ben was physically taken away from the that area by persons unknown.”
Ms Needham said she realised it would be traumatic for Ben to find out what happened to him but she said: “He deserves to know the truth and so do we.”