"We wish to express our deepest sympathies to all of the families of those lost, to the survivors and their families, and to the others impacted by the senseless and unthinkable tragedy that unfolded at Sandy Hook Elementary School," it says. "We cannot begin to comprehend the depth of your sadness and grief. Please know that we care deeply for you and we join with you in sharing your sorrow and pain. We only hope that you receive some measure of comfort in the knowledge that we, and an entire nation, stand with you during this extraordinarily difficult time."
The card has now picked up  more than 1.7 million signatures from around the world, after crossing a million postings in 24 hours. It's been shared on Facebook almost 4 million times. The New York Times reports  that it's the largest gathering of signatures on the website.
[Image: Flickr user Wiertz SÃ©bastien ]