At Sony's PS4 launch party. In New York City's Meat packing district. Andy Gavin, and Jason Rubin founders of Naughty Dog Studios debuted The Last of Us: Left Behind teaser video.
It shows Ellie with her friend Riley as they walk through what looks like a poorly kept carnival. Riley is a character mentioned briefly in the The last of Us. She was with Ellie at a crucial point in Ellie's adventure some time before the events taken place in The Last of Us.