The mysterious disappearance of a 66-year-old Waltham man on Feb. 16 has confounded both police and the man’s family, but no one has given up hope.

Leonard Quirk, who lives at the Francis Cabot Lowell Mill senior apartments at 190 Moody St., was reported missing to Waltham Police on Tuesday, Feb. 23, but has been missing since at least Tuesday, Feb. 16.

“It’s just really odd,” said Leonard Quirk’s son Tim Quirk. “Everyone in town either knows him or knows of him. He walks around the area here almost every day.”

Tim Quirk, who lives in Boston, said his father has lived alone for the past year and a half at 190 Moody St. He said on Feb. 16, his father had left the apartment just after 9 p.m. then returned a few minutes later and walked out of the back door of the apartment, over the footbridge across the river toward the Embassy Cinema and went out of sight.

“For him to just mysteriously walk off and not come back, it just doesn’t make sense,” Quirk said. “His apartment looked like he just stepped out. He wasn’t preparing to go anywhere.”

Quirk said he sent his father a few texts on Feb. 17 or 18, to no response. He later tried to call his father, but his phone was off. While odd, it wasn’t completely out of the ordinary, according to Quirk. When nearly a week went by of unreturned calls and texts, he asked his Aunt Phyllis, who lives in Watertown, to check on him. She alerted the police when Leonard couldn’t be found.

Quirk said he spoke to his father on Monday, Feb. 15, and had spoken to people who saw him on Feb. 16, the day of his disappearance, and said his father had been in great spirits.

Quirk said his father retired a few years ago after a career as an electrical engineer. He said his father had been dealing with health issues recently and had fallen a few times in the past several months, but that nothing like this has happened before.

Ever since his father’s disappearance, Quirk said he and his family members have been trying to find any clues to his whereabouts. Tim Quirk is the oldest of three brothers, and Leonard has two sisters. Quirk said he and his co-workers handed out more than 1,000 flyers in Waltham over the weekend.

He said police are putting a lot of resources into the case and have been doing searches in the Charles River. Quirk said a Waltham police officer told him this is one of the strangest missing persons cases they’ve worked.

“I’ve been trying to stay positive,” Quirk said. “Maybe somehow some way he just had a mental lapse and he’s with someone.”

“More than anything we want to find out where he is,” he said.

Leonard Quirk is described as a white male, 5' 6", 140 pounds, brown eyes, thinning hair and facial scars. He was last seen wearing blue jeans, a green coat and Blue Red Sox baseball cap.

Quirk has asked people who live in the surrounding area to his father’s Francis Cabot Lowell Mill apartment, such as Pine Street, or Newton Street, to check their basements and yards to see if Leonard could have stumbled there.

Anyone with information about Leonard Quirk’s whereabouts is asked to contact the Waltham Police Department at 781-314-3600.