Ben Croll Screening in competition at CPH:DOX, “Girl Gang” offers a behind-the-scenes look at an industry hardly known for reticence. But in this study of adolescent influencer Leonie, her all too eager parents, and the legions of fans liking, sharing and subscribing to the family’s every post, director Susanne Regine Meures offers a more intimate look at the world of modern celebrity.Though set in the suburbs of Berlin, this particular story of social media stardom mirrors those found all around the world. “It is a global phenomenon which actually peaks in the U.S.