Someone else, sharing a photograph of a young man, wrote: “His family has had no news since more than three hours ago #Nice.”
Another friend, desperate to find someone called Lamia, wrote: “Damn, I just saw the news, are you okay? Lamia!!! Respond we are all worried !! Are you in safe?!!”
Another, posted by a man called Pascal, asked for help in finding his cousin Gregoire, missing for two hours after the attack was announced.
A second Twitter account, called SOS Nice, also carried appeals for information. Facebook launched a safety check function to allow users who were in the vicinity of the attack to let their friends know they are safe.