KANSAS CITY, Mo. -- Authorities issued an Amber Alert Tuesday morning for a 13-year-old Missouri boy.

Searchers fanned out in wooded areas Tuesday looking for William Ownby, who disappeared after stepping off his school bus a day earlier.

The FBI is investigating, and officials fear the boy may have been kidnapped.

Authorities said William, who goes by Ben, was last seen late Monday afternoon.

Police said William got off the school bus Monday afternoon and was walking home when a witness saw him being pushed into a white compact pickup truck. Investigators said the pickup is possibly a Nissan or Chevrolet S-10 with a camper shell. The pickup had large rust spots. The pickup truck was last seen heading eastbound on U.S. Highway 50.

Beaufort, where William was last seen, is about 40 miles west of St. Louis.

A friend who left the bus with him told authorities that after the two parted he saw the truck speeding away.

Sheriff Gary Toelke said the boy's parents told authorities it would be out of character for him to run away. Teachers said Ben is an "A" student, "the type of student everyone would like to have," Toelke said.

The boy had a black backpack with him, the sheriff said.

Beaufort Fire Chief William Borgmann said searchers were looking for the boy on foot, horseback and ATV in the hilly area about 60 miles southwest of St. Louis.

William wears glasses and was last seen wearing a St. Louis Rams hooded windbreaker and blue jeans.

Anyone with information on the boy or the pickup truck is asked to call 911 or the Franklin County Sheriff's Department at 636-583-2567.