Divers search icy river for missing Maine toddler Ayla Reynolds

(CBS/AP) WATERVILLE, Maine - Divers searched a half-mile stretch of an icy river on Wednesday but found no sign of missing Maine toddler Ayla Reynolds, who vanished from her father's home over three weeks ago.

Pictures: Ayla Reynolds missing

The number of tips on the possible whereabouts of 20-month-old Ayla has now topped 600, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

"We have ruled out no scenario. We have ruled out no one," McCausland told reporters on Wednesday.

Eighteen divers searched the river while trying to avoid floating chunks of ice. No specific tip had led investigators to the river, but searchers wanted to eliminate the stretch of river between a dam and a bridge as a possibility before snowy weather arrived Thursday, Maine Warden Service Lt. Kevin Adam said.

Ayla was reported missing on Dec. 17, and her disappearance was declared a crime. A $30,000 reward, raised from private donors, is posted for information leading to her return.

Law enforcement officials have searched the woods near the girl's home in Waterville, and nearby Messalonskee Stream was drained nearly dry on Dec. 21 so wardens could get a better look from the ground and sky.

DiPietro said he tries not to let negative thoughts creep into his mind when he considers what might have happened to his daughter.

"I've got to remain hopeful. I've got to remain optimistic. I've got to remain confident they are going to get Ayla home," he said.

All family members and those who were in the house the night Ayla was last seen have been cooperating, Massey said. There were three adults and two children in the house, McCausland said, but investigators have declined to identify any of them other than DiPietro and his daughter.

McCausland said investigators continue encouraging anyone with information, no matter how immaterial it might seem, to call state police.

Complete coverage of Ayla Reynolds on Crimesider