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

Lindsay somehow scored a VIP pass to the concert 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.

No word if Lindsay actually got to spend time with her man-crush this time around.