Adrian Passey, whose son Ryan was stabbed to death in a Stourbridge nightclub in 2017, met the Prime Minister in Westminster to make the case for new measures to support families.
The family said they were left with "nowhere to turn" following Ryan's death, which saw Kobe Murray – now known as Kareem Gayle – cleared of his murder and manslaughter by a jury despite admitting the stabbing.
Mr Passey and family friend Jason Connon outlined a series of recommendations to Justice Minister Tom Pursglove, in a meeting organised by Stourbridge MP Suzanne Webb.
Mr Connon said: "Following the acquittal verdict, we were not offered any appropriate advice or support.
"We were left with nowhere to turn and have had to fight for justice for Ryan on our own.
"This added to the already unbearable loss and the sense of injustice, as well as the subsequent feeling of isolation at being thrown into a 'legal no man's land'.
"A perverse acquittal verdict for a bereaved family is a double trauma and more needs to be done to support victims’ families after trial."
Mr Connon said the meeting had been "very positive" and added: "It was amazing that Boris took the time to speak to us and to understand our campaign.
“He passed on his sympathies and wished us the very best.”
Mr Connon said Mr Pursglove had been “extremely receptive” to the recommendations and had pledged to write to the family outlining those he planned to take forward in the draft Victims' Bill, which will be carried forward in the autumn.
“It’s another step forward in our fight for justice,” Mr Connon said.
“We explained that there should be more support in place, and I think with the Victims' Bill going through Parliament, we’ve certainly given them food for thought.”
As well as improved services for victims' families, the Passey family has called for new measures enabling people to feel safe when giving evidence in major crime trials.
Ms Webb said: “I will do all I can and leave no stone unturned to ensure justice is done, not just for Ryan, but for his family.
“We need to make progress on victim support in these circumstances so that other families do not face the same situation.”
The meeting was arranged after Ms Webb raised the case with Justice Secretary Dominic Raab in the Commons in May.
She told Mr Raab: “The family feel let down by the lack of support after the trial, at the time when they most needed it.
“They have lost their only son, but had no support despite the verdict.”
She requested a meeting “to understand how improvements can be made in the provision of support for victims’ families, not just during an investigation but after the verdict, particularly when a bizarre verdict is given”.
In a bid to improve post-trial support, ministers have announced £4.6m a year in funding for the national homicide service, which provides services including counselling and emotional support that can continue as long as is needed for a bereaved family, including after trial.
Meanwhile, an independent review into the investigation Ryan’s death is progressing in a “timely manner”, his family has revealed.
West Yorkshire Police is conducting the review, which was announced earlier this year following complaints about the way in which West Midlands Police carried out the original investigation.
Mr Connon said they had recently received an update on the progress of the review.
He said: “We have also been in contact with West Yorkshire Police who have informed us their review is now being progressed around the main lines of enquiry and that things are being progressed in a timely manner.”
The Justice for Ryan campaign said the review, which was announced in January after a three-month delay, was a “big step forward”.
The family spent years calling for it after claiming West Midlands Police had not done enough in the initial investigation to secure a guilty verdict against Ryan’s killer.
Russ Whitfield of Liberton Investigations, who is working with the family, said the force may have missed nine lines of inquiry.
He said he is confident the review will unearth “new investigative opportunities”.
Last year the Passey family won a civil case against Ryan's killer, after applying for damages for a death caused by a wrongful act, neglect or default.