“Gossip Girl” first premiered in 2007, but over a decade later, the CW’s teen drama is still a pop culture phenomenon. While Leighton Meester and Blake Lively may be immortalized as Blair and Serena, they’ve gone on to pave successful acting careers of their own. Here’s what Leighton, Blake and their fellow Upper East Siders have been up to post-“Gossip Girl.”