Julian, aged 14, was last seen in Wendover at around 4.15pm today, May 20.
He is 5ft 4in tall, of medium build and was wearing a blue puffer jacket, a grey t-shirt, black tracksuit bottoms and black trainers.
Thames Valley Police Aylesbury Vale said: “Have you seen missing 14-year-old boy Julian?
“We are concerned for Julian’s welfare as he was last seen in Wendover at around 4.15pm today.”
The force added: “If you see Julian, call 999, quoting reference 43260250392.
“Anyone with information on Julian’s whereabouts should make a report on our website.”