Story highlights Charlie Dowd was on his way from San Francisco to Montreal last week

He was not on the train when it arrived in Chicago

Police found his phone, luggage and medication on board

His family says he may be disoriented and needs medical attention

Amtrak police are searching for a retired San Francisco firefighter who went missing while traveling to visit family in Montreal.

Charlie Dowd, 69, left the Bay Area on Wednesday. He last spoke to his son by cell phone Thursday night, saying he was just outside of Denver, Colorado, his family said.

When Dowd's train arrived in Chicago on Friday, he was not on it. His luggage, cell phone and medication were found in his sleeping car, the family said on a Facebook page they set up to find him.

His daughter said Dowd is under a doctor's care and may need medical attention.

"He has medical needs and does need his medication for high blood pressure and heart disease," Jennifer Dowd told CNN affiliate KGO . "He is diabetic, but for medical reasons we obviously want him. We need to know where he is."

An Amtrak conductor may have spoken with Dowd early Friday near Omaha, Nebraska, one of the stops along the route, the family said.

Dowd was confused about his whereabouts and believed he was in an apartment, not on a train, and needed to find the front door, the family said.

Amtrak is investigating the possibility that Dowd got off the train during the night and may have gotten disoriented, and then didn't get back on, the family said.

The train stopped overnight in Fort Morgan, Colorado, and in the Nebraska cities of McCook, Holdrege, Hasting, Lincoln and Omaha.

Amtrak Police said they are working with local police departments at those stops and at BNSF, which owns the railroad.

Jennifer Dowd flew to Omaha on Sunday to look for her father. She said her brother, Kevin, went to Chicago and her cousin, Robert Stevens, is going to all of the stops along the route to search.