"At this moment there are 3,400 people in detention who are Syrian or Iraqi," Nadia Murad Basee Taha told Greek President Prokopis Pavlopoulos during a visit to Athens.
"I call on you to convey my voice to the European Union because thousands of women and small children continue to be held hostage," said the 21-year-old Taha, a member of one of the Iraqi minorities hardest hit by jihadist atrocities.
Taha was abducted by IS fighters in August 2014 from her village in Iraq and held for three months, during which time she was used as a sex slave.
The Yazidis are neither Muslims nor Arabs and follow a unique faith despised by the Islamic State jihadist group. The Kurdish-speaking minority is mostly based around Sinjar mountain in northern Iraq.
In 2014, IS jihadists massacred Yazidis, forced tens of thousands of them to flee, and captured thousands of girls and women as spoils of war.
The UN has said the atrocities committed against the small community may amount to genocide.