Former hostage Ingrid Betancourt has used a rally in Paris to urge Columbian rebels to free all their captives.
She was rescued on 2 July after more than six years in captivity.
Colombian military agents tricked FARC fighters into handing the group over to them.
Thousands gathered near the Eiffel Tower to hear her speak on Sunday. The event was that was one of a series of demonstrations around the world to protest against kidnappings.
FARC has been fighting for more than 40 years, mainly financed by the cocaine trade since the 1980s.
It is holding an estimated 700 hostages. Up to 2,000 more are believed to be held by another rebel group, the National Liberation Army.