Davidson's friends last saw her around 11 a.m. outside Pioneer High School in Ann Arbor, according to WCSO.
Her brother, Anthony Lopez, said someone found the 15-year-old's phone near the high school's tennis courts on Friday and returned it to Davidson's friend.
Davidson is described as 5 ft., 2 in. tall, weighing 100 lbs. She was last seen wearing black, slip-on Ugg boots. (WCSO)
Lopez is also pushing for authorities to release video footage of his sister on a public Ann Arbor bus called "The Ride" traveling on route 29 on Friday afternoon.
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Davidson's family told 7 Action News that Davidson didn't feel well when she got to school on Friday morning and left school shortly after arriving. Video footage apparently shows her returning to school on "The Ride" bus later that afternoon but does not show her going inside the school building.
Missing Adriana Davidson was last seen at Pioneer High School in Ann Arbor, Michigan, on Jan. 27. (WCSO)
"A student told her best friend that they saw her at the bus stop with a man in a black sweatshirt & black pants & ‘they didn’t seem like they knew each other’ but who knows," Lopez wrote in a Saturday update, along with a flyer showing photos and a description of Davidson.
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WCSO Director of Community Engagement Derrick Jackson told 7 Action News that there are "definitely some suspicious pieces to this" missing persons case.
Davidson was reported missing to the sheriff's office around midnight on Sunday, at which point authorities began an active search for the 15-year-old girl.
Adriana Davidson was reported missing to the sheriff's office around midnight on Sunday, at which point authorities began an active search for the 15-year-old girl. (WCSO)
"Everyone please keep posting these pics of Adriana to keep this viral and flooding the internet to keep this fresh in peoples minds we are making progress, so please keep the posts coming and thank you everyone truly thank you!" the 15-year-old's father, John Davidson, wrote in a Monday morning Facebook post.
Davidson is described as 5 ft., 2 in. tall, weighing 100 lbs. She was last seen wearing black, slip-on UGG boots.
Authorities are asking anyone with information about Davidson's whereabouts to contact the Washtenaw Metro Dispatch at 734-994-2911 submit anonymous tips to 734-973-7711.