Sylvester Koroma was hit in the stomach in Birmingham in August 2013 and died in hospital a week later.
Police said his friends had "deserted him in his death".
Appealing for people to come forward and speak to West Midlands Police, his mother, Eunice Koroma, said the last year had been "hell".
Mr Koroma, a father-of-two from the Highfields area, travelled to Birmingham with friends on 10 August last year.
The nightclub had been hosting an event called Circoloco, attended by 4,000 people. The second day was cancelled after the shooting.
Ms Koroma said it had been heartbreaking not knowing who killed her son.
"All of us miss him greatly, especially his sons," she said.
"It's one year on now so I would ask for people to search their hearts, and if they have a conscience, to do the right thing and speak to the police."
Officers previously said they still had no motive for Mr Koroma's death.
Det Ch Insp Sab Johal, from West Midlands Police, said Mr Koroma had been "deserted" by his closest friends.
They had declined to give witness statements to police on the night but he said officers would keep returning to Leicester until they had answers.
"This investigation is not going to go away," he said. "People who know the answers are from this city, and it is those people, who were happy to be with him in his life that have deserted him in his death."
A reward of up to £5,000 has been offered for information to help catch the killers of a Leicester man who was shot outside a nightclub.