Mason Mendoza is a normal teenager from Pennsylvania who, like many high schoolers, enjoys football, baseball and hanging out with friends. When one of his Internet videos goes viral on a new social media app, he is suddenly thrust into the spotlight and forced to make decisions that will dramatically change the future for his entire family. Cat Lansing is a typical soon-to-be teenager from the suburbs of New York City. She wants one thing for her birthday: a new cell phone that lets her surf the web and explore social media like her friends. When she receives her dream phone, her older sister introduces Cat to a new social media app and her life completely changes. When she sees Mason Mendoza's viral video, her infatuation takes fangirling to a new level and she becomes a true diehard fangirl. The first novel in a fictional series based in part on Matthew Espinosa’s experiences as a social media sensation, Diehard Fangirl is both a humorous and realistic look at the power social media has to change and influence the lives of teenagers.