WATERVILLE, Maine — Investigators looking for a 20-month-old girl reported missing a week before Christmas believe someone took her from her father's home, the police chief leading the investigation said Monday.

The comment by Waterville police Chief Joseph Massey marked the first time since the search for Ayla Reynolds began that police have directly said they don't believe she left the home by herself.

"We certainly feel someone took Ayla out of that house," Massey said at a news conference at which he announced a $30,000 reward was being offered for help finding her.

The reward, assembled with donations from people and businesses in the Waterville area, is the biggest ever offered in the state for a missing person, state Department of Public Safety spokesman Steve McCausland said.

Massey and McCausland were joined at their news conference by Waterville attorney John Nale, who appealed for the safe return of Ayla.

"I ask and I plead with the person or persons who have Ayla Reynolds that they please keep her safe and return her safely to us," Nale said.

Hundreds of police officers, game wardens and local residents have searched for Ayla since she was reported missing by her father, Justin DiPietro, on the morning of Dec. 17.

DiPietro told investigators he last saw her when he put her to bed the night before at his home in Waterville, a city of 16,000 residents just north of the state capital, Augusta. He said she was wearing polka dot pajamas with the words "Daddy's Princess" on them and had a cast on her broken left arm.

Ayla ended up with her father after child welfare workers intervened while her mother, Trista Reynolds, checked herself into a 10-day rehabilitation program.

Reynolds, who completed the rehab, had filed court papers that she said she hoped would lead to the return of her daughter. The filing came the day before Ayla was last seen.

Reynolds said she began to question Ayla's care after the girl broke her arm, which police said happened in an accidental fall. She said that she and her family had encouraged child welfare agents to check on Ayla.

DiPietro has said he has "no idea what happened to Ayla or who is responsible." He said last week his family and friends would do "everything we can to assist in this investigation and get Ayla back home."