Rachel GelbThe era of Facebook is an anomalyverified_publisherThe Verge - Ellis Hamburgerdanah boyd’s SXSW keynote is sold out. When it’s over, a dozen fans rush the stage. These fans aren’t young groupies hoping to get a closer glimpse at their favorite rock star, but full-grown adults hoping to hear one more word from boyd. She’s one of the world’s sharpest authorities on how teens …