Arabs, Berbers or Tauregs to be specific.....
Mostly Beydane (white) Moors.
The Tuareg are usually black and there are hardly any rural Berbers. Most slavery happens far away from Tuareg or Berbers however there are some worrying issues with olive groves in the north. More modern slavery there, which of course exits in more developed countries too.
Islam has a slavery problem
Not especially, however the problem exists in less developed and remote parts of the world where Socialism doesn't really exist.
Mohammed had slaves so the practice can't be criticized on moral grounds
It can be and is. Jesus' family probably had them too, btw, as did Washington and Jefferson (who used to rape his slaves).
And, it's clear that residents of the Arabian peninsula think of foreign workers from Asia/Africa as slaves
Some of the worst offenders are white people living in the UAE.
Libya
The chaos of a revolution and two civil wars in a decade has caused problems in every area of life. Makes capitalism without restraint. The slave you read about was probably from Masalata where they allegedly use sub-saharans (mostly male Burkinabians) in the olive groves. I'd guess though that most Libyans have never seen a
Slave though many are descended from them.