The investigation has been going on for almost a month and nothing is ruled out.
Erwan, 18, disappeared on the night of February 10 to 11 in Deux-Sèvres.
The Niort prosecutor's office explained to BFMTV "to work on all the hypotheses".
“We received the family on Monday last week to provide an update on the investigation.
Five investigators are working full-time on the investigations,” added the prosecution.
Erwan disappeared on the night of Saturday February 10 to Sunday February 11 leaving a nightclub, La Morinière, in Moncoutant-sur-Sèvre (Deux-Sèvres).
The Niort public prosecutor's office opened a judicial investigation into a worrying disappearance on February 20.
His smartphone stopped transmitting at 2:50 a.m. that night.
The police have since stepped up their searches and combed the area with the help of a dog, a helicopter and a drone.
Divers from the nautical brigades of La Rochelle and Arcachon surveyed the waterways.
A “moment of solidarity” on Sunday
Drunk, Erwan Blais was kicked out of the establishment by security agents around 1:45 a.m. According to the parents, the bouncers surprised him “in the kitchen, urinating”.
Erwan's family had also filed a complaint against the nightclub for "negligence", according to Le Courrier de l'Ouest.
According to BFMTV, his relatives are organizing a gathering this Sunday, March 10 at 11 a.m. in Saître, his town of origin, which must take place “in a positive and friendly atmosphere to share a moment of solidarity.
Because the search continues and we are not giving up,” Erwan’s family explained to the television channel.