Margaret Peterson Haddix's Missing series

Jonah Skidmore feels like an ordinary thirteen-year-old boy. His family consists of a slightly annoying but smart younger sister named Katherine and a mom and dad who love him unconditionally. Jonah is adopted and has known this fact for a while but it's never been a big deal for him because his parents have always been open about it to him. Life definitely feels normal for Jonah.
  That is, until the mysterious letter arrives--the letter that contains just six words: YOU ARE ONE OF THE MISSING. The letter does not contain a signature or a return address.
  Who sent it? Where did it come from? What does it mean? 

  This book is the first to The Missing series. I grew up with this series, and it has thrilled me. There's comedy, mystery, action, and adventures readers long for.
  The series had no swearing, and just about no violence (although there are epic chase scenes and, as the series goes on, fighting scenes as well).
  I can't talk too much about it (otherwise I'd give the whole story away!), but I do highly recommend this book.
  If you're looking for adventure, the look no further.