“That’s the thing about BookTube,” said Jesse George. “If you’re not a big reader, it inspires you to become one.” Mr. George (bottom row, third from right) and other BookTubers at BookCon in May.Credit...Jenna Clare Photography When Christine Riccio was a teenager growing up in New Jersey, she and her sister would upload videos to YouTube of the two of them being silly, dancing to Britney Spears’