Updated 5/19/2011 at 5:00 p.m.

AURORA, Ill. (CBS) — Police have uncovered new clues in the frantic search for a missing 6-year-old Aurora boy, and they conducted a search in northwest Illinois on Thursday.

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As CBS 2’s Kristyn Hartman reports, police are posting photos of Timmothy Pitzen at rest stops and gas stations close to the Illinois-Iowa border, because they believe his mother used her cell phone there.

The boy’s mother, Amy Fry-Pitzen, later committed suicide in a Rockford motel.

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Police say they grow more concerned as every day passes. But Timmothy’s father, James Pitzen, said Wednesday that he remains hopeful, while extremely concerned.

“I don’t know where he is,” James Pitzen said when asked if he had any ideas where his son might possibly be.

The last time anyone saw Timmothy was Friday afternoon. He was with his mother, Amy Fry-Pitzen, at the Kalahari Resort in the Wisconsin Dells.

Earlier in the day, Fry-Pitzen had pulled her son out of school, and took him to Brookfield Zoo and Key Lime Cove in Gurnee.

“He said him and mom were on vacation,” James Pitzen said.

But sometime later, Fry-Pitzen committed suicide. She was found dead on Saturday in a Rockford motel room after slitting her wrists. Her car has been located, and the family says the fact that Timmothy’s car seat and backpack were not inside may be a positive sign that the boy is with somebody else.

Fry-Pitzen left a note behind indicating that Timmothy was fine, and in the care of unnamed people. Aurora police are talking to friends and relatives of the mother, but since then, there has been no sign of the boy.

“I have a feeling that he’s somewhere safe, that he has not been hurt or injured in any way, and that the people who have him don’t know what’s going on,” James Pitzen said.

His family and police are now trying to get the word out in a new area. The search for Timmothy has shifted to northwest Illinois.

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The Pitzens don’t know anyone there, but it’s where investigators say Amy used a cell phone to call friends and relatives to tell them she and her son were safe.

Aurora Police Lt. Pete Inda says the use of search teams and dogs doesn’t mean investigators are conceding the boy is dead. They’re looking for evidence that ranges from a backpack from the car to clothes and toys the boy’s mother bought in Wisconsin. Authorities conducted searches across a wide area that included Dixon and Sterling and Rock Falls.

“The last time anybody from the family talked to the boy was when he was in the car with the mom in this area of the state,” Inda told reporters.

A spokesman for the city of Aurora later said the search did not yield results.

Could Fry-Pitzen have hurt her son? The boy’s father says no.

“No. She loved that little boy,” James Pitzen said.

Then, when asked about what police termed marital strife, James Pitzen ended the interview. His mother, Linda Pitzen, said James and Amy had no greater issues than any other couple.

As for the suicide, Linda Pitzen said, “Nobody seemed to see this coming. Nobody.”

Linda Pitzen said the hardest thing to watch is “seeing my son not sleep and eat, and just cry.”

While they wait for word on Timmothy, the yard where he plays remains unchanged waiting for him. He left toy trucks in the sandbox.

“This yard is frozen in time. It’s frozen in time waiting for Tim to come home,” Linda Pitzen said.

Timmothy is described as 4 feet 2 inches tall and 70 pounds, with brown hair and brown eyes. He was last seen wearing green shorts and a Spider-Man backpack.

The backpack and his car safety seat are also missing.

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Police say Amy Fry-Pitzen’s past included mental illness.