Some 400 people assembled on a school carpark in Pont-de-Beauvoisin at 8.00am to start the search for traces of Maëlys de Araujo and up to 1,000 more were expected to arrive during the course of the day.
They search was organised by local people not the police, who have already searched the area with the help of sniffer dogs, helicopters, drones and divers, but about 15 gendarmes accompanied them, giving strict instructions as to what to do if they found a possible clue.
A second wave of searchers set off at 9.30am.
Later in the day the gendarmes' switchboard was inundated with calls, sometimes for trivial objects such as cigarette ends or empty bottles, according to Nour-Eddine Ghaoui, one of the organisers.
"A lot of mediums are also calling," he reported. "That contributes to disrupting the switchboard."
Men detained, then released
Two men who were detained for questioning on Thursday and Friday respectively were released on Friday evening.
They are both aged 34 and know each other.
Maëlys was last seen at 3.00am last Sunday at the party in a local community centre that followed the wedding.
Police have opened a kidnapping investigation.
The first man to be detained, a friend of the bridegroom, lives with his parents and is currently on sickness benefit.
He admitted having more contact with the girl than other guests during the evening, according to his lawyer, Bernard Mérau.
He also admitted cleaning his car the day after, according to the lawyer, but said it was because he planned to sell it, a claim that was confirmed by the potential buyer.
It is not known if the second man to be detained attended the party.
Investigators have questioned 250 guests of the wedding and two other parties that took place close by.