Police are "amazed and very happy" that a teenager who has been missing from his home in northern Sydney for more than two months has been found alive.
Matthew Allen, 18, was last seen by his family after leaving his home in Barkala Place in Westleigh in the morning of on November 27 last year.
Police held serious concerns for his welfare after it was discovered he did not take his mobile phone with him, had not accessed his bank accounts or made any contact with his family.
After weeks of extensive searches in surrounding bushland failed to uncover him, Detective Senior Constable from Hornsby Local Area Command Ben Wrigley said they believed he had died.
"Anyone who is missing for that length of time in those kind of conditions - you wouldn't expect to see them again," he told AAP on Monday.
But on Saturday evening two hikers spotted a disorientated man in dense bushland off Elouera Road in Westleigh and went straight to Hornsby Police Station to report the sighting.
After six hours the teen was winched out by a rescue helicopter and flown to Hornsby Hospital where he is recovering from a number of exposure-related injuries, including exhaustion and dehydration.
Detective Wrigley says he's grateful he could finally provide the Allen family with some answers.
"I was amazed and very happy that everything turned out they way that it happened.
"I couldn't believe it," he said.
He said it was "always concerning" looking after such cases, especially when you cannot give the family an answer either way.