The Maine Warden Service said it's searching for a couple from Pennsylvania who haven't been seen since going snowmobiling four days ago in the Moosehead Lake area.

The warden service said it received a missing persons report Monday morning for 41-year-old Clifford Achenbach and his 42-year-old wife, Denise Achenbach, of Pen Argyl, Pa.

Officials said the Achenbachs did not return to their hotel in Moosehead Junction Township, near Greenville, after going out snowmobiling Thursday morning. The couple checked into the Moose Mountain Inn on March 16 and planned to check out Saturday.

Twelve wardens, two warden service aircraft and a Maine Forestry Department helicopter are searching for the couple.