Whitney spent Christmas break in Arizona with her father and then flew from Phoenix to Denver on Jan. 4, landing around 12:30 p.m.
Police told FOX31 last week she did not meet her stepfather at the airport and she has not been in touch with family members.
Monday, police told FOX31 they believe she has run away voluntarily. She has posted several videos on social media saying the same thing.
“Denver Police Department investigators have made progress in the case and while her whereabouts remain unknown, it is believed that she is voluntarily refusing to return home. Investigators are currently working to gather more information to locate her and make sure she is safe,” DPD said.