Authorities say 23-year-old Demi Helenius has not been seen since she left her parents home on Saturday to attend a self-help conference at the Embassy Suites Hotel near Portland International Airport.
A worker at a Dairy Queen restaurant in Lane County later answered Helenius' phone, Thompson said.
Roseburg is about 60 miles south of Creswell, where Helenius' phone was found Saturday night.
The Washington County Sheriff's Office, which sent out the information Tuesday night that Helenius had been found, was the primary agency investigating the case, Lane County Sheriff's Sgt. Carrie Carver had said Tuesday afternoon.
When her family didn't hear from Helenius, her brother made a decision to call her.
We could not have found her without everyone's exhausted efforts. He told them he found the phone in a parking lot after he saw someone throw an object from a vehicle.
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Monday afternoon, authorities said her black 2013 VW bug with OR license plate 855-HNH was found in Cottage Grove.
Authorities said Demi Helenius was found around 8:30 p.m. Tuesday in Roseburg. A "very cursory examination" of the auto at the scene showed no signs of foul place, according to deputies.
Her cell phone was found in a Dairy Queen parking lot a few hours after she went missing from the conference in Portland (top).
Police said they have also spoken with a man who attended the same conference, but did not check back in after the dinner break Saturday night, according to KGW. Cottage Grove is about 130 miles south of Portland. But she hasn't contacted anyone, which is unusual, or been active on social media.
Detectives from the Washington County Sheriff's Office are working with Oregon State Police, Cottage Grove Police and the Lane County Sheriff's Office on the investigation.