Stevie Wonder, Green Day, The Lumineers, The Killers, and The Chainsmokers are set to headline the Sept. 23 Global Citizen Festival, the annual concert in Central Park that blends music and social activism. [...] As in the past, 60,000 tickets are expected to be given out for the festival, essentially as rewards to participants in Global Citizen’s initiatives to end extreme poverty worldwide and tackle other social ills.