An 11-year-old schoolgirl was found murdered in a wood south of Paris over the weekend, sparking shock and a massive search for clues that could lead to the killer.

Louise was found stabbed to death in the Essonne region south of Paris on the night of Friday to Saturday, police said. She had been missing since leaving school on Friday afternoon.

According to a police source, who asked not to be named, Louise had been "hit more than 10 times by an object that could have been a knife", particularly in the torso and neck.

A couple in their twenties were detained Saturday as part of the investigation but were released without any further proceedings at this stage, prosecutors said.

While the circumstances of the killing remain unexplained, it comes with law and order, and in particular crime against children, major issues in French politics and society.

"An innocent life was torn away from life and the love of her family. We are in the process of the investigation, but sadness and anger are overwhelming every French person," said Interior Minister Bruno Retailleau.

Some 120 members of the security forces were deployed on Sunday at the Longjumeau wood where the body was found, seeking any clue that could lead police to the perpetrator, prosecutors said. 

The search ended at nightfall, according to police.