The fear zone - K. R Alexander

If you don't stand up to your fears, they will destroy you. When
five kids are invited to a cemetery at midnight, they think it's
just a prank. When they find a gravestone that instructs them to
dig up a grave, they think it's just a joke. It's no joke. An evil
force is unleashed - a force that takes the shape of their worst
fears. A shark in the water. A ghost in the walls. A nightmare
of being buried alive. A snake about to strike. A sinister clown
waiting in the woods. Once these fears are released, they won't go
away. Not without a fight. . . .