The Gone Series : Fear by Michael Grant

Suddenly it's a world without adults and normal has crashed and burned. When life as you know it ends at 15, everything changes. Night is falling in the FAYZ. Permanently. The gaiaphage has blotted out the sun and the barrier that surrounds the town of Perdido Beach is turning black. It's Sam's worst nightmare. With Astrid still missing and Edilio and Lana struggling to maintain order, Sam and his followers need all the courage they can get. As their world descends into darkness, only real heroes will survive. A tour-de-force from global sensation, Michael Grant, Fear is the fifth book in this bestselling series. "I love this book". (Stephen King).