Investigators continue to work on the case of a 16-year-old Lehigh County boy who disappeared 35 years ago.

Lehigh County District Attorney Jim Martin announced Monday -- the anniversary of Robert Keck's disappearance -- that the investigation is ongoing.

Martin said a search last month in Pike Township, Berks County, didn't turn up anything.

“Based upon information we received from cooperating individuals, various law enforcement agencies participated in a four-day search in May 2014 for evidence in connection with the disappearance of Robert Keck,” Martin said. “Unfortunately, that search proved fruitless.”

Martin and police are asking for the public's help in providing any information about Keck's disappearance.

Keck, who lived in Coopersburg, attended Southern Lehigh High School.

Martin said Chief Robert Coyle of the Upper Saucon Township Police Department, who was a patrolman in 1979 and took the original missing person’s report, has led the investigation for many years.

“Law enforcement agencies are still diligently following up on any leads, and it is my hope that at some point, we will be able to conclude the investigation and provide Robert Keck’s family with answers concerning his disappearance,” Martin said.

Information can be reported to Upper Saucon Township Detective Tom Nicoletti at 610-282-3064 or Lehigh County Detective Joseph Vazquez at 610-782-3831.