Two suspects freed after French girl Maelys de Araujo disappears from wedding in French Alps

Maelys de Araujo, nine, disappeared during a wedding in the French Alps. Photo / AP

A French prosecutor has opened a formal kidnapping investigation in the disappearance of a nine-year-old girl who went missing from a wedding celebration in the Alps last weekend.

Maelys de Araujo was last seen in the early hours of Sunday at a community hall where the wedding was held in Pont-de-Beauvoisin, a village 50 kilometres north of Grenoble.

Grenoble deputy prosecutor Laurent Becuywe said on Saturday that no leads would be cast aside in the investigation, including the possibility that the girl was a victim of an accident, said news.com.au.

Two men, both 34, were released without charges on Friday night after being questioned, he said. They were detained on Thursday and Friday.

Investigators sought explanation from the men on "some elements," he said. "As things stand, it was decided these elements were not enough to justify charges". He declined to elaborate.

Mr Becuywe said police have questioned more than 200 potential witnesses and carried out about 40 house searches in recent days.

"The absolute priority is to find the young Maelys", he added.

Until Saturday, the girl's disappearance was subject to a preliminary investigation. The formal investigation has two judges assigned to the case.

Scores of police, search and rescue teams, divers and cavers have spent the week trawling through the heavily wooded area for signs of her.

On Saturday morning, more than 1200 people were expected to participate in a "citizens' search" for signs of the girl's whereabouts, a private initiative organised via social media networks, and co-ordinated by about 15 gendarmes.

A first group of about 400 volunteers braved heavy rain to gather at a parking lot at the local high school at 8am local time, before donning yellow safety vests and splitting up into groups to search the surrounding forest.

"We're here for her, to find her," said a person close to Maelys's family who was taking part. "We're still hoping to find her safe and sound."

"It's really horrible ... we cannot remain indifferent. We have come here for a family facing a shameful situation," said Frederic, a volunteer who had come with his wife to help trace the girl.

The volunteer teams were expected to relay each other throughout the day, and a hotline has been set up to signal any clues, though police underscored that the areas had already been examined.

Police have interviewed about 250 people since Sunday, including most of the 180 guests at the wedding, as well as several others who attended parties held the same night at a nearby bar and church hall.

Police also requisitioned photos and videos taken by wedding guests to look for any unusual activity.

Sniffer dogs lost the scent from Maelys's cuddly toy in a car park outside the venue, raising fears she was kidnapped and whisked away by car.

"We're getting farther and farther away from the site of the disappearance," a source close to the inquiry told AFP. "We still think that she was probably taken away in a vehicle."

Police chief Yves Marzin said authorities are also examining photos and videos taken that day, as well as all calls to the area.

"It is like looking for a needle in a haystack, extremely tedious work but important," he said.