The Tomorrow Code by Brian Falkner

Best friends Tane Williams and Rebecca Richards are contemplating the cosmos one lazy afternoon, when they start to wonder about the possibility of time travel.  Being an accomplished teen scientist, Rebecca speculates that although physical objects can't be transported through time, perhaps data can - the secret, she postulates, lies in "quantum foam."  Sure enough, as they pursue Rebecca's idea, they start to perceive codes in the quantum foam.

What the codes turn out to be are messages from their future selves.  When the first message turns out to be the winning lottery numbers, Tane must enlist the help of his older brother Harley "Fatboy" to collect the prize money.  As the messages continue, the three realize that the future Tane and Rebecca are sending a warning, and that action must be taken to save the human race.

Eager to get more information, the kids head to a research facility in the Bay of Islands.  When they return after their initial visit, they are shocked to discover all of the inhabitants of the island have simply disappeared without a trace.  Meanwhile, a mysterious fog has enveloped the northern tip of New Zealand's North Island.  When the fog moves on, all humans in its wake are destroyed.

It is up to Tane, Rebecca and Fatboy to solve the mystery of the human-eating fog and to take action to save the world.  But can they decode the messages and implement a plan in time?  Find out in this brisk page-turner of an adventure!