DETROIT, MI - It often starts with a colorful flyer on social media, with messages like “no guns,” “f— that curfew” and “your park, your voice, your takeover.” One post can quickly spread to hundreds — even thousands — of young people, fueling “teen takeovers” that have become a defining trend of the summer. The gatherings are typically organized on social media and occasionally have ended in fights, vandalism and shootings in downtown Detroit.