At least 129 people are dead and 100 seriously injured in the deadliest attacks on France since World War Two.
Eighty people were killed at an Eagles of Death Metal concert at the Bataclan concert hall in Paris.
Attackers took hostages before blowing themselves up after security forces stormed the hall.
People were shot dead at restaurants and bars at five other sites in Paris.
On Twitter people are using hashtags including #PrayforParis, #PrayForPeace and #StandWithParis to show their support for the victims and their families.
The hashtag #JeSuisParis is being used again as it was after the Charlie Hebdo killings in January, in which 12 people died.
A sketch of the Eiffel Tower as a peace sign is also being posted and users are changing their profile pictures.
Other hashtags on Twitter expressed outrage at the attacks like #TerrorismHasNoReligion.
Other images being shared include a black peace ribbon laid over the French flag, a pair of hands clasped together in prayer around the Eiffel Tower, and a famous landmarks covered in red, white and blue.
On November 13, the hashtag #PorteOuverte, or Door Open, was used for anyone who wanted to find refuge in Paris after the attacks.
In the US, some used the hashtag #strandedinUS to offer shelter for people who can’t travel back to France because of flight restrictions.
Facebook users are being offered a safety check feature called Paris Terror Attacks to let their friends and family know they’re safe, or to try to locate people they know in the city.
On Twitter the hashtag #Bataclan is being used to try to track down loved ones.
Paris is now under tight security with schools and universities closed.
There will also be three days of national mourning in France after the attacks.
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