Police and FBI officers intensified their search Monday for a missing 6-year-old Aurora boy who police say wandered away from home on New Year’s Eve as the temperature was expected to drop into the upper teens.

The Colorado Bureau of Investigation issued an Amber alert Monday for David Puckett because of the cold weather and the amount of time the boy has been missing, Aurora police spokesman Crystal McCoy said.

As night fell Monday, police held a news briefing as FBI agents again canvassed the neighborhood where the boy lived with his family, which includes three juvenile siblings. Authorities planned to continue their search well into the night, McCoy said.

David disappeared from his home in the 15700 block of Amherst Avenue around 5:30 p.m. New Year’s Eve. Some family members were home, McCoy said. She did not disclose who was there.

Police also said someone outside the family had seen the boy the day he went missing, but McCoy did not elaborate on who that was or where or when the sighting was made.

The family searched for David for an hour before calling Aurora police. And the Jefferson County Sheriff’s Office had its bloodhound on the trail within an hour of Aurora police receiving the call, McCoy said.

There has been no indication that police have found any sign of David since the search began.

Although police said they have no indication of foul play, officials emphasized the investigation was ongoing, McCoy said. The FBI joined the investigation because of the increased resources the bureau can provide.

The FBI has assigned 50 agents to the case, including one who is highly specialized in missing children searches, said Deborah Sherman, an FBI spokeswoman. The FBI has set up a command post although Aurora police remains the lead agency in the search.

More than 100 officers joined the searched on Monday, including the Arapahoe County water rescue team and officers from area police and sheriffs departments.

Police have contacted registered sex offenders who live in the area and have searched nearby bodies of water looking for any signs of cracked ice, McCoy said. Police and FBI agents canvassed neighborhoods and set up checkpoints to notify motorists of the search.

David’s family has cooperated with police, who have searched the family home multiple times, McCoy said.

On Monday evening, the CBI issued a statement about the decision to issue an Amber Alert three days after the boy was first reported missing.

While the circumstances surrounding David’s disappearance have not changed, the bureau decided to activate the alert out of an abundance of caution.

The alert is one tool that can be used to disseminate information that already has been released about the boy and his disappearance, the CBI statement said. The statement praised Aurora police, saying that department “has been exceptional” in using the media and social media to relay information about the search.

Aurora police have said they consulted with the CBI about a possible Amber Alert since the child first was reported missing. However, David’s disappearance had not met the criteria for Amber Alert notifications.

The CBI will continue to communicate with Aurora police and provide resources as needed, the statement said.

Earlier Monday, volunteers were called to join the search, which has been confined to a 2.5-mile area. By mid-afternoon, police had asked volunteers to stop looking for Puckett because their efforts could disrupt the work of the bloodhounds who were on the trail again.

“We are continuing to do thorough searches of the neighborhood,” McCoy said. “We will notify people once again when we’re ready for the community to start searching.”

Authorities were also looking for residential and commercial video to aid in their investigation, McCoy said. She asked anyone who finds any evidence that they think could be related to David’s disappearance to call police rather than pick items up or post images of them on social media.

Police were growing more concerned Monday night as the search extended beyond 48 hours and with temperatures headed toward the teens. The boy was not appropriately dressed to be out all night in freezing temperatures.

David attends Dartmouth Elementary, where he wandered away once before. Previous reports that the boy had wandered away from home more than once do not appear to be true. McCoy said Aurora Public Schools were making mental health professionals available to staff and students.

“At this time we believed he wandered off,” McCoy said. “We have one documented instance where he wandered off from school.”

Aurora police Chief Nick Metz said on Sunday there was no evidence of a kidnapping.

“That could change as the investigation moves forward,” Metz said.

David is about 4 feet tall and weighs 48 pounds. He has light brown hair and blue-green eyes. He was last seen wearing green camouflage pants, a black T-shirt, orange boots and a tan girl’s coat, according to police.

The boy’s mother made a tearful plea Sunday for the public’s help, emphasizing that the coat was not very thick.

“If you guys can, please help me find him. If you see him, please call the police immediately. If, by chance, you picked him up last night because you thought it would be best please bring my baby home,” she said.

Aurora police are asking those with information to call any of their tip lines: 303-739-1865, 303-739-1868 or 303-739-1870.