Franklin W. Dixon 
Children of the Lost [EPUB ebook] 
Book One in the Lost Mystery Trilogy

The boys go on a chilling missioncamping in the woods where children have suddenly begun to disappear. Every time a child disappears, the word "LOST" has appeared outside their tentand they are never heard from again. The boys think theyve got things covered; theyre ATAC agents after all. But when an "L" appears outside their tent their first night in the woods, things take a turn for the creepy.