Two men were arrested in connection with the disappearance of Andrew Gosden more than 14 years ago.
A 45-year-old was arrested on suspicion of kidnap, human trafficking and the possession of indecent images of children; while a 38-year-old was held on suspicion of kidnap and human trafficking, a spokesman said.
Both have now been released under investigation while inquiries continue.
Andrew, who will now be 28, vanished on September 14 2007, with the case becoming one of the most high-profile missing person probes in the North.
He emptied his bank account of about £200 and went to Doncaster station, where he bought a one-way ticket to London King’s Cross.
His family and police believe he boarded a train at 9.35am, arriving at Kings Cross at 11.20am.
CCTV images captured at the station – and later released by South Yorkshire Police – made up the last known sighting of Andrew, with no further information about his movements corroborated by officers.
His family have staged a high profile campaign over the years to keep their son in the public eye and to help the families of other missing people.
Our priority at this time is supporting Andrew’s family while we work through this new line of enquiry in the investigation
Det Insp Andy Knowles, South Yorkshire Police
A post on the campaign’s Twitter feed, which referenced a local newspaper story on the arrests, said on Tuesday: “It is a difficult time for Andrew’s family who currently know no more than what is written in the article.
“Police investigations will be ongoing for quite a while and we respectfully ask you to give them your support and consideration whilst this takes place.”
Detective Inspector Andy Knowles, from South Yorkshire Police, said: “Our priority at this time is supporting Andrew’s family while we work through this new line of enquiry in the investigation.
“We are in close contact with them and they ask that their privacy is respected as our investigation continues.
“We have made numerous appeals over the years to find out where Andrew is and what happened to him when he disappeared. I would encourage anyone with any information they have not yet reported to come forward.”