The tweets and Facebook messages are meant to let everyone know we're all in this together. Sentiments President Obama echoed in his speech Friday evening.
"This is an attack, not just on Paris, it's an attack not just on the people of France, it's an attack on all of humanity and the universal values that we share," the president said shortly after news of the attacks spread.
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Hashtags like these aren't an abnormal sight after similarly tragic events, especially in Paris. The current wave of solidarity echoes use of the hashtag #JeSuisCharlie after the attacks on satirical magazine Charlie Hebdo earlier this year.
One World Trade Center also lit up in the colors of the French flag Friday. The Paris attack is the second-most deadly terrorist strike on a Western city since 9/11.
This video includes images from Getty Images and music from Josh Woodward / CC BY 3.0.