The 13th Reality by James Dashner series

What if every time you made a choice that had a significant consequence, a new, alternate reality was created — the life that would've been had you made the other choice? What if those new realities were in danger? What if it fell to you to save all the realities?

A boy named Atticus "'Tick'" Higginbottom is a normal 13-year-old until he gets a letter from Alaska, signed 'M.G.' Tick learns that something deadly is about to happen and could result in the destruction of reality itself. Tick then follows clues and solves riddles in more letters, soon meeting new friends and journeying into other realities- alternate worlds that are created every time a choice is made. Not knowing what dangers lie ahead Tick and his friends take on a journey that could be life-threatening.