David Kelly, who is now 59 years old, has had no contact with any of his family since he vanished in September, 1984.
He had been living in Kimbolton Crescent in Stevenage, Hertfordshire, but worked as a carpenter in Bedfordshire in the months before he went missing.
His brother John Kelly said: “David, if you see this appeal I want you to know that your brothers and sisters miss you very much and have never stopped thinking about you.
“It would be lovely to know you are alive, well and happy. John and Kim.”
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At the time of his disappearance David was described as being white, 5ft 7ins tall, of thin build and clean shaven.
He is originally from southern Ireland and spoke with a southern Irish accent.
PC Stuart Barnett from the Missing Person’s Unit said: “Sadly previous appeals have not brought any information and, whilst it has been decades since his disappearance, I would urge anyone who may have known David who hasn’t already contacted police, to please call us with any information.
“I would also ask David to make contact if he sees this appeal.”
If you can help find David, please call PC Barnett via the Herts Police non-emergency number 101 or email [email protected]