Lindsay Lohan to Max George -- SURPRISE!!! I'm Backstage at Your Concert

Lindsay Lohan is still hot on the trail of Max George -- following him ... like a common groupie ... from NYC to Philadelphia last night, and even popped up backstage at a 'Wanted' gig.

Lindsay somehow scored a VIP pass to the Jingle Ball -- where The Wanted performed -- and was seen signing autographs for fans.

Of course, the last time LiLo tried cozying up to Max ... she got sloppy drunk, rejected by the boy-bander, and ended up in handcuffs after fighting with a woman inside of an NYC nightclub.