Hopes that missing Australian soldier Captain Paul McKay would appear at a New Jersey airport for the first leg of his scheduled flight back to Australia have been dashed.
"At this point he has not boarded a plane," Saranac Lake police sergeant James Law told AAP on Wednesday.
Capt McKay was last seen on New Year's Eve walking on railroad tracks in the Adirondack Mountains in upstate New York.
A ground search of the dense forest area involving Saranac Lake police, state rangers and volunteers has failed to find any clues to where Capt McKay might be.
He has been suffering post-traumatic stress disorder after a tour of Afghanistan and is on leave from the Australian Army.
Capt McKay, 31, purchased an Australia to the US round-trip airfare, with the return leg beginning from New Jersey's Newark Liberty International Airport to Los Angeles on Wednesday afternoon.
He was then scheduled to fly from LA to Australia on Wednesday evening.
The Transport Security Administration (TSA), airlines and airports have been alerted to be on the lookout for Canberra-based Capt McKay.
Banks will alert authorities if he uses a credit card.
"We have everybody watching and looking with the hope we would find him, but we haven't heard from anybody," Sgt Law said.
Capt McKay went missing when the northeast US was hit by the polar vortex, bringing minus 30 degree temperatures and snow storms, but Saranac Lake police chief Bruce Nason said Capt McKay's Army training gave searchers and his family hope he could survive.
"Based upon his experiences, if anybody has a chance of going into this wooded area and coming out it is him," Chief Nason said.
"He has some experience.
"We are hoping he got slowed down by the weather.
"I remain optimistic.
"If I wasn't, we wouldn't be looking that hard and if it was my child I would want everybody to remain optimistic and we are.
"We are committed to continue the search for as long as it takes."
Capt McKay sent an email to his father on December 30.
In the email, Capt McKay said he was leaving all of his possessions to his father.