Working quietly behind the scenes, the Teen Challenge team help about 400 people every week who have problems, including drug addiction, alcoholism and gambling.
On a Friday afternoon, they visit the Wyndford flats in Maryhill before making a late-night trip to the Barras and the Bellgrove Hotel.
As many as 40 men and women have been known to board the small bus, particularly on the evening visits, desperately looking for someone to talk to or a bite to eat.
The charity was originally founded in the US but a Glasgow branch was started in 1990 and has expanded to cover the former Strathclyde area, including Greenock, Paisley and Clydebank.
They provide hot drinks and food at more than 21 sites across the west of Scotland and often refer people to special rehabilitation centres that help them to beat their addictions and get back on their feet.
In the past year, six people from Glasgow have been sent to rehab through the charity and many more have been given advice, clothing and food.
One of the rehab "graduates" is Michael Sturrock, 33, who is now responsible for the bus service after turning his life around more than five years ago.
Michael was addicted to heroin for 14 years before coming across Teen Challenge.
He said: "I remember at a young age thinking that heroin was a drug I would never touch - it was a dirty drug, I knew the effects of it.
"However, I tried it once and it led to a 14-year addiction.
"Someone told me about the Teen Challenge residential programme about 5½ years ago and I did one of its Christian programmes and my life has never been the same."
During one afternoon in Maryhill, the bus received visits from a number of locals keen to talk to someone about their problems.
Some had issues with drugs while others were just lonely and needed some company.
One woman had been in an abusive relationship and had been visiting the Teen Challenge bus regularly for the past few months.
She said: "These guys are really helping me so much.
"I don't know what I would do without them.
"I met them in Gallowgate for the first time. It was pelting with rain and they said, 'Come in' and since then I have been coming.
"It is just nice to talk to somebody, I have got nobody to talk to."
Despite still battling with drug addiction, the woman would like to eventually do voluntary or charity work and said the volunteers give her motivation to turn her life around.
In the evenings, the bus is often mobbed with people from the Bellgrove Hotel, a designated hostel for the homeless.
But Michael has witnessed on his weekly trips to the East End site that its residents' problems can often become worse .
Michael said: "People we worked with go in homeless and after being surrounded by alcohol and drugs they think 'Why not?', and develop other problems."
One of the charity's volunteers warned of the dangers of recreational drug use after meeting youngsters in Maryhill who reminded him of himself.
The man, who did not want to be named, spoke about how easy it was to fall into serious drug addictions.
He said: "I started smoking cannabis at a young age, I must have been first year of secondary school.
"I remember seeing a few teenagers on the bus last week and they said they would never be heroin addicts, they would never do that, but when I was talking to them I felt like it was just me when I was that age.
"You think it won't go any further."
The group often stay out until 1am helping the city's most vulnerable people - those who feel they no longer have anywhere else to turn.
They share their stories and help others to overcome their addictions without asking for anything in return.
For more information on Teen Challenge see: www.tcstrathclyde.co.uk