Ed Sheeran has 9.4 million Twitter followers and some of the most devoted fans in music, but even the star singer-songwriter was shocked by his introduction to the fandom surrounding John Green's novel "The Fault In Our Stars." Sheeran's announcement last month that he'd written a song for the coming movie adaptation received 48,700 retweets, his most ever, he says.

Sheeran is set to feed that following Wednesday night when he performs his song live for the first time at a concert showcase for the movie's soundtrack....