Research by homelessness charity Centrepoint and Warwick University found that after 12 months on the programme, just one in 80 young people with complex needs had obtained a permanent employment contract.
The participants with extra needs had experience of homelessness or being in care, a disability or learning difficulty and a history of drug or alcohol abuse.
In addition, 35 per cent had dropped out of the welfare system completely, becoming "hidden Neet" (not in education, employment or training).
The initiative provides six months of intensive support to 18- to 21-year-olds making a claim to Universal Credit Full Service and was rolled out to all Jobcentres in December 2018.
It includes workshops and interventions, identifies any training needs and support to improve job search, application and interview skills.
Centrepoint's research also found that while 24 per cent had some form of employment, for 44 per cent of this group it was informal, cash-in-hand work.
Of those in formal employment, 44 per cent were claiming Universal Credit to top up their average annual wages of £6,000.
In addition, participants were more than 10 per cent more likely to be sanctioned than their peers who were not on the programme.
Centrepoint said this indicates that vulnerable young people are being rushed onto the programme when they are not ready or able to benefit from it and are expected to remain on it despite significant barriers to participation.
The charity added that this results in young people who are most in need of support being subject to increased sanctioning, dropping out and consequently losing access to any support they might have received through the programme.
It added that once these young people have dropped out, it becomes increasingly difficult to re-engage them, possibly only when a crisis forces them to seek much more immediate and costly interventions.
The findings contrast with statistics from the Department for Work & Pensions (DWP) released today, which found that, of those that finished the programme between January and March, 64 per cent found employment, and 56 per cent did so within two months of leaving it.
There were around 63,000 participants between October 2018 and April 2019.
Centrepoint's chief executive Seyi Obakin said the programme is failing to help the most disadvantaged young people and called on the government to undertake a full impact assessment, ensuring it is properly funded.
"Our research raises serious concerns about the high drop-out rate and increased risk of benefit sanctions for disadvantaged young people," added Obakin.
"Without the right safeguards in place there is a large risk that those with complex needs will not only fail to gain the new skills they need but will be actively pushed away from support in other areas of their lives."
The DWP has been contacted for comment.