David Bird, 55, vanished Saturday afternoon in Long Hill in northwestern New Jersey, NJ.com reported Thursday. Investigators said that Bird, who is required to take medication for a liver transplant, left it at home.
NBC News reported that Bird's credit card was used Wednesday in Mexico. NBC also quoted "a source close to the family" who said they believe his disappearance might be connected to his work covering the Organization of Petroleum Exporting Countries.
A friend at the Bird home told NJ.com there are "a lot of theories going round."
The friend said the family wanted everything to go through Long Hill police.
In the days since Bird's disappearance, police, volunteers and members of other local and Morris County agencies have searched the Passaic River, woods, fields and swamps in the area.
"While search operations may appear to be scaling down we can assure you that the investigative aspects are scaling up," the police department said in a statement on its website. "Morris County Prosecutor's Office detectives are with Long Hill Police investigators leading the investigation."