Sammy Keyes and the Runaway Elf — Wendelin Van Draanen

I should have just said forget it!

Instead, Sammy Keyes is stuck cruising the streets of Santa Martina on a Christmas float filled with dogs in antlers. But when three pranksters sabotage the parade and send the dogs scurrying, it's up to Sammy to find a prize Pomeranian. The blasted dog's been kidnapped, and the Pom's owner will stop at nothing to make Sammy get her back.

Whoever's got that dog had better watch out! Sammy Keyes is nosing around, and she'll do whatever it takes to make sure the bad guys pay...