They were all considered misfits. There was just something about them that apparently, wasn't normal.
Justin was abused.
Sam has no family.
Mia had depression.
Liam was bullied.
They all went to middle school together, and in the beginning of seventh grade they decide to run away. They could get hurt out there, since the day after they left there was an anouncement that a murderer was on the loose, and he was nearby. They could get hurt. They were in danger. But what did they know? They're just kids.