Joseph Kintau, the head of the Papua New Guinea Civil Aviation Authority, told The Associated Press said the wreckage was in an "extremely difficult" terrain, and search and rescue officials were trying to access the site.
"The aircraft crash wreckage has been located and the rescue team has been dispatched to give us a report," he said, adding that rescuers had picked up a faint radio signal but saw no movement.
The plane vanished on Tuesday morning as it approached a remote airport near Papua New Guinea's Kokoda Track, a historic Second World War trail that traverses more than 100km of mountainous, rugged terrain.
Airlines PNG said in a statement later that the helicopter crew that spotted the downed plane saw "no immediate signs of activity" near the wreckage.
Allen Tyson, a spokesman for the airline, said the plane had radioed in its approach to the airstrip but never landed.
Nine Australians, one Japanese and three Papua New Guineans were among the 11 passengers and two crew on the short flight.
Kokoda is the site of a well-known hiking trail especially popular with visitors from Australia, whose troops fought a bloody battle against Japan in the area during World War II.
At least 19 planes have crashed since 2000 in Papua New Guinea, whose rugged terrain and lack of internal connecting roads make air travel crucial for its six million citizens.