The biggest slave owners were the Turks. Every fifth Christian boy had to be given as slave to the Turkish sultan (dervisme).
The larges slave market was Kaffa (now Feodosia) on Crimea, where Ukrainian, Russian, Polish and Rumanian slaves were sold to Turks. Women as sexual slaves, men for servitude. Turkish harems were almost exclusively “staffed” by European Christian women, as enslaving Muslims is prohibited by Koran.
Even during WWI, Armenian women slaves were sold in Istanbul.
On the other hand, In Wester Europe, the Trinitarian order
https://en.wikipedia.org/wiki/Trinitarians
Was established solely to free Christian slaves from Muslim capturers.
Europeans captured and enslaved by Muslims (Turks, Arabs, Berbers) go to millions.
In the book Don Quixote by Cervantes, he tells the story of a young boy captured by the Turks. He survived by pretending to be a girl till rescued by the Spanish.
He did it because he found the Turks had a sexual preference for young boys.