The police arrested a 22-year-old man on Tuesday in a house in Montélimar (Drôme).
The individual is suspected of having prostituted a 19-year-old mentally retarded girl.
The suspect was taken into custody.
The girl was also there.
She was taken to the hospital, indicates France Bleu Drôme Ardèche.
The alert was given by the victim's 16-year-old sister.
Worried about not having heard from her eldest, she had explored the social networks of the latter.
She had discovered messages exchanged with men, mentioning sexual intercourse and accompanied by photos.
The 19-year-old woman had said that she was a prostitute and had mentioned an individual acting as her pimp.
The teenager had warned the police and geolocated her sister on Snapchat.
In addition to the suspect and the young woman, cash, phones and used condoms were found at the scene.
Five indictments for the prostitution of a teenager in Compiègne
Justice
Lyon: Very young women kidnapped and forced into prostitution in Montpellier
Valence
Auvergne-Rhône-Alpes
Prostitution
Pimping
Miscellaneous facts