Without a trace / by Robin Caroll Miller.

Enhanced descriptions from Syndetics:

Sam Sanderson is an independent, resourceful, high-tech cheerleader. She dreams of becoming an award-winning journalist like her mother, so she's always looking for articles to publish in her middle-school paper (where she secretly hopes to become chief editor). With a police officer for a father, Sam is in no short supply of writing material.

In the fourth book of the Faithgirlz Samantha Sanderson series, Sam's friend Tam Lee is missing. As the days pass, all clues seem to point to something sinister in Sam's opinion. Sam must decide whether to do what everyone wants her to and let law enforcement continue to work as though Tam is a run-away. Or should Sam follow her heart and keep poking around looking for more clues

The Samantha Sanderson series is about an ordinary girl with extraordinary dreams. Each book touches on a crime straight from headlines, from bomb threats to bullying, while following Samantha and her friends as they navigate middle-school and questions of faith.