(Estacada, OR)  --  Clackamas County authorities are still looking for an 18-year-old who vanished Sunday morning.  Brandon Powell of Estacada hasn't been seen since around 5:30 a.m. Sunday, when he was wearing only a pair of blue pajama bottoms.  Sheriff's deputies say Powell took off suffering from an apparent panic attack after taking a high-potency dab of marijuana.  Authorities say he may have headed for the Clackamas River.  Anyone with helpful information is asked to call 911.