A Hard Nut To Crack by Christine Isley-Farmer

An upset Robbie shows up on the doorstep of the home of his friends, Chloe, Boomer, and Nana Weathers. His dog, Hoppy, disappeared from his backyard. When Hoppy hasn't returned by the next day, family and friends spring into action. Boomer makes friends with two squirrels in a squirrel network who offer to help with the search. Will the piling-up clues lead to a reunion for Hoppy and Robbie?