Penpal by Dathan Auerbach. This the most disturbing book that has come to my hands in a while. My jaw dropped to the end of the second tale “Balloons”. An elementary school teacher asks the kids to use balloons to send letters to start a penpal correspondence. A kid starts receiving letters and photos of him taken by somebody who seems to be uncomfortably close to his house.
This is a horror novel. I like it but I think it works better as a collection of short stories. This book can be read as a whole on reddit. I believe it is the first book by the author and is self-published.