At St. Martin in the Fields recently, in the heart of central London, a choir lifted its voices out of the depths of despair. Nearly every member has endured the anguish of a missing loved one – children mostly. Some, like Peter Boxell's son Lee, disappeared decades ago without a trace.

"If he is in heaven, then I just pray that he can hear us and that he will know that we're still thinking of him, that we still love him," Boxell said.

They call themselves the Missing People Choir – 30 or so voices from every walk of life. Most had never sung a day in their lives, until music producer James Hawkins volunteered to start the choir back in 2014.

The Missing People Choir performing in St. Martin in the Fields in London. CBS News

"To be eye-to-eye with family members that are there singing to you, who in their heads they're singing to their missing loved one, that's incredibly powerful," Hawkins said.

"There's almost like an instant understanding," said correspondent Lee Cowan.

"Absolutely. And everything is unspoken."

Their goal is to raise awareness of the roughly 180,000 people who are reported missing in the U.K. every year, including their own loved ones.

Boxell's 15-year-old son, Lee, left home in 1988 to go to a soccer match in South London. He hasn't been seen since.

Cowan said, "All these years, though, you never moved away, did you?"

"No, we couldn't bear to move from this house," Boxell said. "We always hoped that Lee would come home one day. Well, we still do."

For decades, he and his wife Christine have waited for any news of his whereabouts. And in all that time, Lee's room has stood just as he left it – his school blazer on a hanger, homework unfinished on his desk.

"We've not been able to grieve, NO, because we don't know for sure what happened to Lee," Boxell said. "I've got that little bit of hope that he hasn't been murdered. I just cling onto that last hope."

One night in 2013, Boxell had a dream that he was singing a song he had written for Lee. With the help of James Hawkins, whom he had met through the Missing People charity, they literally turned that dream into a reality.

Peter Boxell sings, as part of the Missing People Choir. Missing People

Over and over he practiced his song for his son, knowing full well he couldn't really carry a tune. But that didn't matter. At the annual Missing People charity's event, Boxell got up and sang it – belting out his solo as if he'd been singing all his life.

"Lord, help me find my son!"

He said, "Being able to sing about my son released all those bottled-up emotions. I mean, as a bloke, I don't like to get emotional, really. But when I was singing in front of 800 people, it was just so uplifting and cathartic."

Hawkins said, "We saw a transformation happening with Peter. You know, there was more color coming back to his eyes, and his personality."

If singing helped Boxell, Hawkins thought, it might help others, too, like Rosalind Hodgkiss and her eldest daughter, Nina Gross.

Alice Gross vanished in August of 2014; she'd told her mom she was going out to see friends, and was never heard from again. She was 14.

"Ribbons were going all over the country, you know, and posters were going all over the country," said Rosalind.

Nina said, "While she was missing, I woke up every morning, the first thing I would be saying is, 'Is she home?' You dream every night that she came home, then you wake up and you're like, 'It's not happened yet.'"

A month passed before Alice's body was finally found in a canal. She had been murdered.

Alice's talent for music, however, lives on. She wrote a song, "Don't Let It Go Away," two years before she disappeared, which was then performed by the Missing People Choir:

For Ros and Nina, music has proven to be the one thing that soothes that wound that will never heal.

Nina said, "It brings you that bit closer to her. I feel like when I'm singing, I have that in common with her. I can hear her voice, and I can talk to her and say, 'Oh, I'm really not as good as you are, but you know, trying.'"

Cowan said, "As healing as it is, it's gotta be difficult, though, too?"

"Yeah, and you get some rehearsals which are more difficult than others."

Rosalind said, "Sometimes the moments where you feel most connected, it's also the moment where you feel the saddest because then you're aware, I'm aware, more of the loss."

There is comfort in their togetherness. Each of the choir members feels it. And while practice may not always mean perfect, their hard work is getting noticed.

In 2017 the choir got the chance to sing to their biggest audience yet, on "Britain's Got Talent."

There wasn't a dry eye in the house.

The performance was so well-received the choir released "I Miss You" as a single this past December. But the best part was that all the publicity did exactly what the choir hoped it would: It brought at least six missing people back home.

Ju Blencowe was one of them. "Without the work of the Missing People Choir, I wouldn't be here," she said.

"You don't think so?" Cowan asked.

"I know so."

Blencowe went missing after her mother passed away. She had been caring for her for more than a decade, and was so grief-stricken about losing her she had a mental breakdown, and wandered away in a fog.

"I just thought how easy it is to just become a lost person, a faceless person, someone without a story," she said.

But somehow the memory of hearing the Missing People Choir made her realize that she, too, was missed. "The whole mixture of emotion and love within that choir, to make it sing out so beautifully, touched my heart, and brought me home," she said.

The hope that that can happen more often is just what sends Peter Boxell up to his son's empty bedroom to practice.

"Lean on Me" takes on a whole new meaning coming from such a place of pain.

"Lean on me

when you're not strong

I'll be your friend

Someone to carry on…"

James Hawkins said, "There's something about that communal singing together that has a healing power and property to it which I don't think I even want to know why it does it. I'm happy that it does."

A choir singing their hearts out while healing them, too.

Members of the Missing People Choir. CBS News

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Story produced by Deirdre Cohen.