Hunger by Michael Grant (Gone #2)

Food supplies are dwindling and Sam Temple is facing mutiny from the kids in Perdido Beach. Driven into town by hunger, Caine and his psychotic sidekick are spreading fear and violence.
And deep in the ground, the biggest danger of all is getting hungry.
The GONE series is Lord of the Flies for the 21st century. In turns breathtaking, harrowing, and utterly terrifying. Its complex characters and moral dilemmas will delight fans of The Hunger Games, Divergent and The Maze Runner. This is dystopian fiction at its best