The man, named only as Jean-Edouard, was staying at his uncle's home in the southern port city of Marseille when he took his life by shooting himself in the head on Saturday, reported local newspaper La Provence.
Initial reports suggested the man, who used the alias Redjohn, had been talking to a psychologist at the time he killed himself but Wednesday's Le Parisien newspaper claimed these were untrue and he had been talking to another user named Ravioli.
Ravioli contacted other users as well as the police after the incident. Another user contacted one of the site's administrators, based in Canada, who was able to track down the man's identity.
The website alerted Interpol and local police visited the man's home in Castres in the south west of the country.
His parents told police that their son was away, staying with family in Marseille. In the meantime, the man's body had been found in the apartment in the Trois-Lucs district of the city.
Newspaper Le Parisien reported the Doctissimo website as saying the man was not a frequent user.
"This man was not a regular," said Christophe Clément, a spokesman for the site. "He had created his profile quite recently and had hardly any previous history of using the site."
The newspaper also claimed that the image of the dead man was left on the site for several hours.
"Other internet users were able to see the images," said one site regular, according to the newspaper. "The image of his head lying on the desk after his death stayed up for several hours before the site took it down."
The site's managers have kept details of the dead man's activity before his death which they will hand to police.
"This was a very regrettable incident," said Christophe Clément. "It's clear that the links and exchanges that happen between people on our site have managed to prevent many more suicides than they've caused."