However during a briefing to journalists on Monday, Mr Jeffrey was asked whether there were any signs of Mr Cantlie or a Japanese prisoner and replied: "no, not yet".
Mr Cantlie was one of a number of high-profile hostages held by Isil and used in its propaganda videos. In early videos, he appeared in an orange jumpsuit like other Western hostages. In later videos, he was dressed in civilian clothes and acted like a journalist reporting on conditions inside the so-called caliphate.
He last appeared in a video from Mosul in December 2016 and there has been no confirmation of his status for more than two years.
Earlier this year Britain’s Security Minister Ben Wallace was accused of being “genuinely irresponsible” after he claimed Mr Cantlie was still alive.
Mr Wallace insisted Mr Cantlie was alive when asked about the photographer during a meeting with foreign reporters at the Home Office - the first official confirmation that Mr Cantlie is believed to be alive.
Mr Jeffrey also said the US does not know the whereabouts of Isil's leader, Abu Bakr al-Baghdadi, who is rumoured to be hiding in the Anbar desert in western Iraq.
"No we don't know where he is, and finding the top leadership of Isis or other terrorist groups is always a priority," Mr Jeffrey told a briefing at the US State Department.
While Isil has now lost all the urban territory it once held, it continues to have a presence in the desert of both Syria and Iraq.
Mr Jeffrey underscored this point, said Islamic State's loss of its last territorial stronghold in Syria over the weekend was a "great day" but he added that the fight against the group will go on and US forces would remain in Syria in limited numbers to help.
James Jeffrey, the US special envoy for Syria, has revealed there are no signs of the British journalist John Cantlie and other hostages since the last pocket of Islamic State territory was recaptured this weekend.
Mr Cantlie, a British photographer, was kidnapped six years ago by the Islamic State of Iraq and the Levant (Isil), alongside American journalist James Foley.
While Mr Foley was beheaded on camera in 2014, Mr Cantlie was kept alive by Isil and forced to front a series of propaganda videos where he spoke in English to the camera.
On Saturday, the Western-backed Syrian Democratic Forces (SDF) announced they had retaken the last remaining are of Isil-controlled territory, sparking fresh hope over the fate of the group's hostages.
The Free John Cantlie campaign, a support group run by his family, said on Saturday: "Stay strong John. We still hold out hope of good news".