Divers combed the waters of Portland Harbor near Union Wharf on Monday in their search for a Saco man who disappeared early New Year’s Day in Portland’s Old Port.

James E. Dyer, 23, was last seen by friends on Fore Street as they left a bar, headed for their car parked on the waterfront.

“I know he’s out there. I know he’s alive,” said Amy Dyer, his mother, who lives in Old Orchard Beach. “I can feel him. I’m staying positive he’s going to be found.”

Investigators on Monday also collected security video from Old Port businesses, trying to make sure the videos were not being taped over, as some systems do automatically.

So far, none of the video that has been removed and viewed has included a sighting of Dyer.

Efforts to use cellphone tower data to find Dyer’s cellphone have not been successful. The phone’s battery was low when Dyer headed into Portland with friends for New Year’s Eve festivities, said Saco Police Chief Bradley Paul.

“If that phone battery is completely expended, that’s the same from our perspective as if he shut the phone off,” Paul said.

The search for Dyer is technically a Saco case, because he is missing from that community, Paul said. However, because he was last seen in Portland, that city’s department has taken the lead on the case.

“Quite frankly, he went missing from Portland,” Paul said. “Portland has really pulled out all the stops. … Portland has been treating this case as one of their own.”

Saco dispatched two detectives to work with Portland police, but that is not an indication they believe Dyer was intentionally harmed, he said.

“We have no indication at this point there is any kind of foul play involved,” Paul said. He said detectives were assigned to the case because it is a missing person and because detectives can more easily work in different jurisdictions, as a case such as this one requires.

During low tide Monday afternoon, the Portland fireboat Cavallaro and a smaller fire department boat with a search dog scoured the waters between Portland’s piers for Dyer’s remains. Police divers swam along the boats and piers near Union Wharf. That is where the car in which Dyer had planned to get a ride home was parked.

The water search was called off at dark.

Saco Sgt. Corey Huntress said police are searching the water because that is one of the logical places where Dyer might have ended up.

“In the past there have been unfortunate incidents when people have fallen off piers and into the water (in Portland),” he said. There have been cases where a person who was missing from the waterfront for several days eventually was found among the pilings.

Amy Dyer said she is glad that police from multiple agencies and the Coast Guard have joined the search, but she hopes they find no sign of her son in the water.

“I don’t want them to find anything, for sure. That’s where I don’t want success,” she said. “But I’m glad they’re doing everything they can. … It’s kind of a waiting game at this point.”

Investigators planned to review security video for clues about Dyer’s disappearance, but the process is painstaking. Nighttime video images can sometimes be of poor quality and there were throngs of New Year’s Eve revelers in the streets as the Old Port bars closed at 2 a.m., making it more difficult to pick out individuals.

“We’re trying to get what we can to piece back together” Dyer’s movements, Huntress said.

Paul said police will focus their search on the areas where they know Dyer was during the night.

The friends who were with Dyer that night told police they had been at the Old Port Tavern on Moulton Street, then went to The Pearl on Fore Street, leaving at 1:45 a.m. They got separated from Dyer in the crowds outside The Pearl and waited on Union Wharf, where they had parked their car. Dyer’s friends have been cooperative, Paul said.

Dyer’s mother reported him missing at 11 p.m. Friday after he failed to show up at 7 p.m. for his job as night operations manager at the Hannaford supermarket in Kennebunk.

While she tries to stay positive, Amy Dyer said her son is clearly in trouble.

“I definitely think something is wrong,” she said. “I don’t think he’s of his right mind.” Otherwise he would have made some effort to contact his family, she said.

“He’s a strong kid, a good kid,” she said. “His friends and family and the whole community are doing everything to look for him.”

Police are soliciting information from anyone who saw Dyer on Friday after about 1:30 a.m., Paul said. Dyer was wearing a red flannel shirt, tan pants and a New England Patriots hat with the old-style logo, Paul said.

Police ask anyone with information to call 284-4535.