(Portland, OR)  --  Police are asking the public for help in their investigation of a 2015 missing person case.  The Multnomah County Sheriff's Office says Tiffany Bettis AKA Melinda Smith went missing in March of 2015.  She was last seen at the Quality Inn in Gresham.  Police say she left behind three children, and family members tell investigators they don't believe she would have left them behind willingly.  Anyone with information on her disappearance is urged to contact police.