Steven Clark, 23, was last seen on December 28, 1992, near his home in Marske, near Redcar.
Police believe he is dead and arrested his parents in 2020 on suspicion of mur*der, but they were released without charge.
The family has joined the charity Missing People in their search for answers.
Mr Clark, who had a disability that prevented him from using his left arm and walked with a limp, had gone for a walk with his mother along the beach to Saltburn.
She last saw him entering a public restroom around 15:00, and for many years, that was the last time she saw him.
However, in September 2020, Cleveland Police reported that a woman saw him later that day near his home.
Mr Clark was last seen wearing a maroon crew neck jumper, a navy-blue parka with a fur hood, blue denim jeans, and grey trainers. He was described as 6ft 3in tall, of medium build, with blue eyes and dark brown hair.
His parents, Doris and Charles Orr, and younger sister Victoria Orr, according to Missing People, “worked tirelessly to keep search efforts for Steven alive in the hopes that he will be found safe and well.”
“Steven going missing has been a living nightmare for all of us,” Ms Orr said.
“Our relationship as a family was love-filled, Steven and I couldn’t have wished for a happier childhood.”
She described her brother as a “avid Arsenal fan” and music lover who played the baritone euphonium, was a “great swimmer,” and “loved computing and IT.”
“He had a great sense of humour, an infectious laugh – you couldn’t help but laugh when being around him,” she said.
She claimed that his disappearance devastated the family, and that they did not celebrate Christmas for eight years because it “just felt wrong without Steven.”
Mr Clark was born in the United Kingdom and raised in South Africa until 1990, when his family relocated to Guildford, Surrey, before settling in Marske.
The family said in a statement released to coincide with the new appeal, “Dealing with ambiguous loss is a life sentence.”
“The constant, agonizing limbo of not knowing is a horrible thing to have to deal with.”
“We still hope he will walk through the door one day, but we recognize that it is becoming increasingly unlikely with each passing year.”
“We just want to know what happened.”
Mr Clark’s case had “no active lines of inquiry,” according to Det Ch Insp Shaun Page, but the force would “continue to respond to intelligence and information that may help us locate Steven.”
He stated that any information, “however insignificant it may appear,” should be reported.