The trio, a man of 19 and two boys aged 17, from north west London, are being held by authorities in the country.
Scotland Yard said counter terrorism officers were told on Friday that the two boys had gone missing and were believed to be travelling to Syria.
A spokesman said: “Inquiries revealed that they had travelled with a third male, aged 19 years.
“Officers alerted the Turkish authorities who were able to intercept all three males, preventing travel to Syria. They remain in detention in Turkey. The families have been kept informed of developments.”
It comes just weeks after an international police hunt was launched to find three London schoolgirls who travelled to Istanbul on their journey to Syria.
However, Shamima Begum, 15, Amira Abase, also 15, and Kadiza Sultana, 16, who are pupils at Bethnal Green Academy, are now feared to have reached the conflict zone to become so-called “jihadi brides” with Islamic State.