It makes me sad when people say they haven't read a book all summer. Summer is one of the best times to read something! Read something fun! Here's a few ideas to get a reluctant reader reading something this summer:
Getting excited about a book is key, and an air conditioned bookstore (with treats from the cafe) can help stir up some excitement. Reluctant readers also respond well to choice, so letting them choose their own book can help a lot. Be encouraging, but also guide them a little to books they can handle. Short, action filled, or possible romance-centered books can be winners. Also look for books that are popular or best-sellers. They might have heard of them, or seen movies based on the book.
Have reading material available, just lying around when reluctant readers are looking for something to do. This doesn't just have to be books! Magazines go a long way too, especially ones on topics that are interesting to your reluctant reader--they'll be much more inclined to pick them up. And reading can happen anywhere--at the pool, in the car, the backyard, etc.
Try to not force anything on a reluctant reader. Pretty much every student at some point in their school career has been bombarded by summer reading lists, or been severely pressured to read during the summer. Make reading something fun by appealing to their interests. Maybe it's a biography on their favorite sports star, or graphic novels. Books that have been turned into movies or TV shows. Books that everyone is talking about. Whatever works, summertime is fun time and reading should be too!