21-year-old Michael Smith and 19-year-old Crystal Smith haven't been seen since Wednesday morning.
The family says they left on foot from Kenduskeag and were going to Bangor.
A family member says they are both special needs and have never had to take care of themselves.
State police have been notified and there is an active missing persons investigation for the two.
Michael is 5'5" with brown hair and brown eyes and wears glasses.
Crystal is 5'6" with dirty blonde hair and blue eyes.
Anyone with more information should contact Trooper Andrew Peirson at the State Police Bangor barracks at 973-3700.