The FBI is assisting in the search for missing Wall Street Journal reporter David Bird, who was last seen leaving his northern New Jersey home more than a week ago.

Barbara Woodruff of the FBI's Newark office confirmed to FoxNews.com that the agency is helping the Long Hill Township Police Department locate Bird, who disappeared Jan. 11 after leaving his Morris County, N.J., home to go on a short walk.

Bird, a 55-year-old avid walker and scout leader, left his cellphone and daily medication at home. Morris County was hit with heavy rain that day, after Bird set out for a walk, and portions of the surrounding Passaic River flooded area swamps. Bird, a father of two who had a liver transplant nearly 10 years ago, was recovering from a gastrointestinal virus when he left for the walk wearing a red rain jacket, according to authorities. He took medication twice a day for his liver transplant but was not carrying it when he left the house.

Expansive searches of the surrounding land -- including swamps and portions of the Passaic River -- have yielded no sign of Bird. A law enforcement source told FoxNews.com that there is no evidence to indicate foul play but that "it hasn't been ruled out."

"Anything is possible," said the source, who is not authorized to speak publicly about the case.

Police on Sunday were searching nearby railroad tracks for any clues, according to the Newark Star-Ledger, which also reported that police were looking closely at activity on Bird's computers and phone.

Bird works as a reporter for the Wall Street Journal, covering OPEC, a collection of oil-rich countries. He also worked for Dow Jones & Co., the newspaper's publisher, for more than 20 years.

Woodruff said the FBI was assisting in the hunt for Bird, but said the Long Hill Township Police Department remains the lead agency in the case. She declined to elaborate further on any details of the investigation.

Bird is described as white, 6 foot, 1 inch tall and weighing approximately 200 pounds. He was last seen wearing a distinct bright red jacket with two yellow zippers.

Anyone with information on Bird's whereabouts is being urged to call The Long Hill Township Police Department at 908-647-1800.