Harry and the Potters, a Norwood band that writes songs inspired by the fictional wizard, were surrounded by dozens of fans onstage as they ended their performance at Wilson Middle School in Natick on Saturday night. The Potters were there to help celebrate the launch of “This Star Won’t Go Out,” a book by and about Esther Earl , the Quincy teenager who inspired John Green’s 2012 bestseller, “The Fault in Our Stars.” Earl died in 2010 of thyroid cancer at 16. “This Star Won’t Go Out,” which was released last week, is a collection of her journals, drawings, letters, and pictures, and includes essays by family members and her Boston Children’s Hospital doctor. Earl was a huge fan of Harry and the Potters. Wellesley Books hosted the Saturday-night celebration.