Internet users posted poignant appeals on Twitter to find their loved ones who had been at the scenes of the bloodshed, including at the Stade de France stadium and a rock gig at the Bataclan theatre.
“If anyone has news of Lola, aged 17, at #Bataclan this evening, contact us,” read one post, while another expressed concern for a friend Thibault, who was also at the concert. “He's not getting back to me: help me”, it read.
Other Twitter feeds remained ominously silent after announcing the start of the concert at the Bataclan concert hall, where at least 82 people were later killed by gunmen wielding AK47s.
Eight attackers struck numerous locations around the capital, leaving at least 120 people dead on Friday night, the bloodiest such incident in Europe for more than a decade.
Thousands of Parisians used the hashtag #PorteOuverte (open door) to organize places to stay for people who had been left stranded — particularly in areas that had been attacked.
The hashtag was re-posted 480,000 times as the hours passed with the city on lock down, making it the second-most used keyword on Twitter in France after #fusillade (shooting) which was used 700,000 times.
“If people are stranded, I can accommodate two of three people on Rue des Martyrs,” offered one user, while WroteGabDeLioncourt said: “Our sofa is always available for two/three people in Maraichers”.
Others set up an emergency website “porteouverte.eu
” to help people find temporary shelter.
Meanwhile, Facebook launched a check-in feature to let people know that friends in Paris were safe.
The “Paris Terror Attacks” safety check let people signal whether they were out of harm's way, then notified all those they know at the leading social network.
“Quickly find and connect with friends in the area,” a message at the Facebook Safety Check page read. “Mark them safe if you know they're OK.”
The feature also allowed people to check which friends listed as being in Paris had not yet checked in as safe.
“We are shocked and saddened by the events unfolding in Paris,” a Facebook spokesman told AFP.
“Communication is critical in these moments both for people there and for their friends and families anxious for news.”
The death toll in the “unprecedented” series of attacks across Paris climbed through the night on Friday.
Police said around 100 people were killed at the Bataclan music venue in eastern Paris alone, where one witness said an attacker yelled “Allahu Akbar” (God is greatest).