(Portland, OR)  --  The search for a missing Portland-area woman is over after police found her safe and in good health.  The Washington County Sheriff's Office says a public tip led them to 23-year-old Demi Helenius in Roseburg last night.  Helenius had disappeared Saturday night after attending the Landmark Worldwide Forum near the Portland Airport.  Police found the woman's car about ten miles south of Creswell on the I-5 corridor in the town of Cottage Grove Monday, and her cell phone turned up at a Creswell Dairy Queen the night she disappeared.