The search for a 13-year-old Boy Scout who fell into the fast-moving Yellowstone River (search) expanded Sunday as nearly 200 park officials and volunteers scoured the river by kayak and on foot.

Luke Sanburg, of Helena, Mont., was pushing logs into the river with other scouts Friday when one of the logs clipped his legs and knocked him into the river. He was last seen floating downstream with his head above water, the National Park Service (search) said.

A white tennis shoe, fitting the description of one worn by Luke, was found about five miles downstream.

Sunday's search expanded north into Montana (search) from a 14-mile section of the river between Knowles Falls and a bridge at Corwin Springs, Mont. A team of kayakers were combing the river while park officials and volunteers focused on the banks, said Cheryl Matthews, a park spokeswoman.

Luke's parents were also helping with the search, she said.

Luke and six members of his troop were camping in the northern part of the park, about six miles from Gardiner, Mont., a park gateway. Three adults were with the boys, Matthews said.

The Yellowstone incident came just days after 11-year-old Scout Brennan Hawkins was found in good condition after spending four days wandering the Utah wilderness.