Kix guitarist Ronnie Younkins went missing Saturday and was just found ... but he's not in great condition.
We're told Ronnie's bandmates went to pick him up in Maryland for a gig in Pennsylvania but he was nowhere in sight. They tried to call him ... but nothing.
The remaining Kix band members went on to play the show at the Hummel's Wharf Fire Company, and broke the news to the crowd.
We're told the band was incredibly worried ... for good reason.
Younkins has a history of substance abuse -- he went to rehab for alcohol in 2015.
Ronnie was found Sunday morning "not in great condition and very upset." It's unclear what happened.