On December 26, at before 23:45 GMT, Cody Fisher, a non-league football player and coach of school sports, was fatally hurt inside The Crane nightclub.
He was declared dead around 30 minutes later despite efforts to rescue him, according to West Midlands Police.
“They have crushed our hearts; I have lost my best friend,” his family remarked.
The police are seeking witnesses.
The incident took place at the club on Adderley Street in Digbeth during a Boxing Day concert that included renowned techno DJ Marco Carola.
In Birmingham-area non-league football, Mr. Fisher was a left back.
He is pictured wearing the Bromsgrove uniform in a West Midlands police release. He also played for Stratford Town and Stourbridge.
According to posts on social media and in the local media, he had attended the Birmingham City FC Academy and was also a trainee with Walsall.
Police believe Mr Fisher was approached by a group before being stabbed and are urging anyone in the club to get in touch.
“We know there were hundreds of people in the nightclub at the time,” added Det Insp Thurgood.
“While we’ve spoken to a number of them already, we still need to hear from anyone who was there and who witnessed or even filmed what happened.”
One clubber told the PA news agency there were “groups of lads” who were “looking to cause trouble”.
“As soon as me and my friends walked in, we got a very weird vibe and the atmosphere wasn’t good,” said Sydnee Power, 23, from Birmingham.
Another attendee from Wolverhampton said the event was a “disaster waiting to happen”.
“Me and the friend I was with, not once did we get asked to clear our pockets out even though mine were full. I had cargo trousers on with pockets full,” he said.
“They didn’t even touch me whilst searching me, they just followed the outline of my body with their hands then tapped me to say go on through.
“Obviously you want everyone to have a good time and enjoy themselves [but] when we got in I said to my friend: ‘That’s the worst search I’ve ever seen’. Anyone could have brought anything in.”