The body of a missing Lansford teen was found Tuesday night in Schuylkill Township.

Schuylkill County coroner Dr. David J. Moylan confirmed a body found in a rugged area of Tuscarora is that of a 17-year-old girl missing since early Sunday.The body of Cassidy Derr was found in the area of Locust Mountain in Schuylkill Township, off Old Route 209, he said.The location is "up on a mountain," he said. "They used all-terrain vehicles to get to the body."State police at Frackville were at the scene. Moylan said Cassidy's body would be brought to Simon Kramer Institute, New Philadelphia, where he will examine it.Derr's family last saw her on Saturday, before she headed out to the woods of Schuylkill Township to attend a party in a secluded space on Locust Mountain, between Tuscarora and Brockton. An argument in the wee hours of Sunday morning led Derr to walk away from her friends and head out toward Tamaqua, according to police.She kept in touch with other friends, via Snapchat and text, finally admitting she was lost somewhere along old Route 209. That last message was sent at 7:51 a.m. Sunday. No one had seen or heard from her since.The insulin-dependent Type 1 diabetic was supposed to start school in Panther Valley Monday morning, after her family recently moved to Lansford. Previously, Cassidy attended Tamaqua Area High School and was home-schooled for a while.Her family spread word of her disappearance on Sunday, and the search began in earnest on Monday morning.Late Monday afternoon, the North East Search and Rescue group had five dog teams staging at the Tuscarora ball fields, asking Cassidy's family and friends to suspend their own searches to avoid confusing the K-9s.During the early evening, a state police helicopter equipped with thermal imaging flew over the area but was unable to find any sign of Cassidy. While state police were searching by air, the dog teams moved out.Also searching were members of the Tuscarora Fire Company, who used four-wheelers to cover the utility line area and mine roads, while Schuylkill County Emergency Management Coordinator John Matz provided detailed maps of the area.Kathy Kunkel contributed to this report.