George Jack Temperley-Wells was last seen in the Marina area of Antalya, having travelled from Darlington with his mother on June 29.
Police have serious concerns for his welfare and are urging anyone in contact with them to reach out to the authorities.
George is described as having red hair, a pale complexion and dark eyes, while Ms Temperley is 28 years old and slim, with long, dark hair and dark eyes.
They are likely to have spent time in Turkey with the four-year-old’s father, 41-year-old Scott Nigel Wells.
Anyone in the UK with information can call Durham Constabulary on 101, quoting incident number 325 of June 30, while those in Turkey can go to a local police station or call the emergency number on 112 / 115.