Erwan B. has been missing since an evening at a nightclub last weekend in Moncoutant-sur-Sèvre.
His family filed a complaint against the establishment for "failure to assist a person in danger", according to the Niort public prosecutor's office. Prosecutor Julien Wattebled indicated on Friday that he had opened an investigation, entrusted to the gendarmerie. Dozens of gendarmes, including divers, helped by dogs, a drone and a helicopter, took part in the search.