Ryan Passey's parents say they hope it will make young club-goers think twice before carrying a knife.
Ryan was 24 when he was fatally stabbed in Chicago's nightclub in Stourbridge town centre in August 2017. Kobe Murray, 19, from Dudley, stood trial for his murder but was cleared by a jury at Birmingham Crown court last year.
Under a photograph of a smiling Ryan, the plaque reads: "When you think of me, smile, share my stories, remember all the happy times, and know that I will live forever in your hearts. Enjoy your life, like I did."
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Addressing the crowd, John Passey recalled his nephew's "zest for life, laughter and sometimes downright cheekiness".
Bouquets of flowers were laid and candles lit at the spot which has become a shrine in the two years since Ryan's death.
His family continues to fight to get the law changed to allow for more grounds to appeal against acquittals in serious criminal cases.
Ryan's mother, Gillian Taylor, 53, said the family was overwhelmed by the turn-out on Saturday, which "shows how much he was loved".
She said she avoids the venue, outside the Ryemarket shopping centre on the High Street, because its memories distress her.
"It's been over two years and I still struggle every day," she revealed. "I get up and go to work but it's only because I've got him in my head, saying 'Come on Mom, pull yourself together'.
"Ryan couldn't pass anyone without saying hello, he was so nice. He's such a massive loss. He was my only son but we come from a big family so the knock-on effect has been huge."
Speaking of the plaque, she said: "People forget what happened, and looking at this will remind them and wake them up. If we can stop someone else getting stabbed that's all I can hope for."
Ryan's stepfather Philip Taylor added: "We can't afford to get complacent."
Chicago’s shut in February last year after more than 3,500 people signed a petition calling for its closure but it is due to reopen soon under a new name, Soda Lounge.
However the owners have agreed to implement stringent security measures and to omit a dedicated dance floor.
Jason Connon, from the Justice for Ryan campaign, said the criminal justice system was seriously failing the victims of knife crime and their families.
The campaigners have raised their concerns in meetings with the former Home Secretary Sajid Javid and chair of the All-Party Parliamentary Group for miscarriages of justice Barry Sheerman.
They have also met senior prosecutors and the West Midlands' Assistant Chief Constable Jayne Meir who have all voiced sympathy for group's work.
A fighting fund pays for the legal fees and funds the work of private detectives still investigating Ryan's death.
Mr Connon said: "We are next planning to meet with the Ministry of Justice and hope to get a further meeting with the new Home Secretary once a new Government is elected. We will never stop fighting for Ryan."
In September, the family joined the relatives of Reagan Asbury, knifed to death after a boxing event in in Walsall last year, and James Brindley, fatally stabbed in Aldridge, in 2017, took part in a march as part of a Tackling Knife Crime Together event.
Ryan's father Adrian Passey said: "We're still hoping we'll have our day back in court and justice will be served for Ryan, which he deserves."