The last time anyone saw 7 year-old Kyron Horman, he was walking down the hall of his Portland, Oregon elementary school to a classroom 150 feet away. Four days later, nobody knows where he's gone, or why.

Horman's stepmother, Terri Moulton Horman, drove him at Skyline Elementary School last Friday morning around 8 a.m. There they toured a student science fair together, and Horman showed off his project on Red-eyed tree frogs. (And Terri snapped the picture above and put it on Facebook.) Terri last saw him walking down the hall in a blue "CSI" T-shirt, headed to his classroom just 150 feet away after the 8:45 bell.

For some reason, Kyron never made it to class. When Kyron didn't show up at the bus stop after school that day, Terri called Skyline Elementary and learned he'd been marked absent. No one at the school had seen Kyron since Terri sent him to class earlier that morning. She immediately called 911, and now the search for Kyron is in its fourth day. Authorities have received 1,200 tips, scoured the surrounding area with a helicopter and multiple rescue crews, and interviewed 200 of Kyron's classmates and their families. (Skyline only has around 300 students.)

But so far detectives haven't even turned up enough evidence to suspect an abduction. And a family friend told ABC News that "He's not the type of child who would just go out of school and go searching or wandering around... He's just a timid, sweet boy." When asked if police had identified any persons of interest, a sheriff responded: "In this type of situation, I think everyone is of interest to us." [OregonLive][CNN][ABC]