They're out there somewhere.

That's what authorities hope as they expand their search for Mary Ellen Walters, 68, and Ada Wasson, 80, two elderly women who vanished nearly three weeks ago after leaving their close-knit retirement community for a day of outlet-store shopping.

Authorities, volunteers and relatives have driven up and down roads covering thousands of square miles of Ohio, Kentucky and Indiana and flown over the region. They've looked for credit card activity, studied store videotapes, checked under bridges and passed out thousands of fliers.

Nothing has turned up to indicate there whereabouts or whether they may have been victims of foul play.

"It may be the next square mile we search," said Brad Nixon, Walters' son-in-law. "The optimism is reduced ... but how do you stop?"

Warren County Sheriff's Maj. John Newsom calls it one of the broadest investigations ever in this area about midway between Dayton and Cincinnati.

Walter and Wasson are believed to have left Otterbein Retirement Living Community in Lebanon on April 19, headed to a J.C. Penney outlet store in either Columbus or Carrollton, Ky., with Wasson driving her 2000 Chevrolet Impala, Newsom said. They were reported missing three days later, when Walters' daughter came to pick her up for an evening out and found worried neighbors.

"That's all we think about," said Dorothy Pfeiffer, Walters' next-door neighbor. "We're kind of like zombies now."

Walters is a mother of three whose husband was in Florida visiting his own ailing mother; Wasson is a widow with no children.

They had set out for Carrollton's outlet mall, some 80 miles to the southwest, earlier that week but got lost. They had lunch at a restaurant in Kentucky, then came back to Otterbein, laughing about it, said Walters' daughter, Cindy Nixon, and neighbors.

The two women preferred driving scenic highways rather than Interstate 71. That complicates the search.

Authorities know Wasson filled her car's gas tank the night of April 18, and they left some time the next day.

There, the trail goes cold.

There has been no activity on their credit or bank cards, police say. They didn't take any luggage or give any other signs of planning for a long trip. Neighbors said Walters normally would ask them to watch her dog, a Schnauzer mix named Suzie, if she planned to be away for long.

Police and family members spent hours studying parking lot and store videotapes at the mall in Carrollton without success.

"We've looked at this from every angle we can think of," said Newsom. Police have been meeting every morning to discuss the investigation and have consulted with FBI experts.

Wasson at times became confused, while Walters was limited by knee problems, neighbors said.

It's the first such missing person case for Otterbein, where people enjoy living on their own, said chief executive Bob Benson.

Cindy Nixon remains optimistic the women will be found safe. She said family members hope to help others by compiling a database of contacts and things they've learned in the search — such as making sure neighbors know how to contact children.

Others are less hopeful.

"At first the phone lines buzzed, 'Have you heard anything? Have you heard anything?'" said the Rev. Ronald Payne, who succeeded Walters as pastor of the Milford Center United Methodist Church in northwest Ohio when she retired three years ago. "Now people are afraid the worst has happened."

Newsom said police are still making daily efforts, but soon will have to begin scaling back the search.

"We always want to be able to fix things for people," he said Friday. "We haven't been able to fix this."

The Associated Press contributed to this report.