Police in Idaho have found a cellphone belonging to 17-year-old Tylee Ryan, who, along with her 7-year-old adopted brother, JJ Vallow, hasn't been seen since September, a source close to the investigation told CBS News. It appears her phone was found in Hawaii with her mother, Lori Vallow, who has been considered a person of interest in the case.

Lori and her new husband, Chad Daybell, traveled from Idaho after police conducted a welfare check on their home in November and were found in Hawaii in January.

Ryan's phone was used several times after she disappeared, but it's unclear who was using it, CBS News correspondent Jonathan Vigliotti reports.

On October 25, more than a month after the 17-year-old disappeared, a text was allegedly sent from her phone to a worried friend: "hi. miss you guys too …luv ya." The recipient said it didn't sound like her.

Also in October, two small Venmo payments were reportedly sent from Ryan's account to a family member.

The discovery of Ryan's phone comes after items belonging to her and JJ were found abandoned inside a storage facility.

Both of Lori Vallow and Daybell's former spouses, as well as Vallow's brother, died under what authorities call suspicious circumstances over the past eight months.

Both Vallow and Daybell have denied any wrongdoing.