(Portland, OR)  --  The search continues today for a missing Portland woman.  The Washington County Sheriff's Office says 23-year-old Demi Helenius was last seen Saturday night at the Landmark Worldwide Forum at the Embassy Suites Hotel near the Portland Airport.  Her parents say she didn't return home Saturday night, and officials say she didn't attend the conference yesterday.  Police say an unidentified man gave the woman's cell phone to a Dairy Queen worker in Creswell as he passed through the drive-through Saturday night.  Police found the woman's car about ten miles south of Creswell on the I-5 corridor in the town of Cottage Grove.