The mother of a missing 15-year-old Oregon girl believes she ran away with an older man she had been communicating with online for several months.

Kyrsten Roth's mother Michelle Long last saw her on Dec. 3, KATU-TV reported Sunday.

One of the girl's friends saw her get into a truck with a man in his 20s in her hometown of Gresham, Ore. -- about 15 miles east of Portland -- on Wednesday.

Michelle Long said her daughter had told her she was interested in a boy at her high school, but phone records showed that she had been calling someone in California for several months before she disappeared.

"Kyrsten did not run away, she ran to someone," she said. "We don't know anything about this person."

Police in Gresham are investigating Kyrsten's disappearance, and her mother has also been in contact with authorities in California, according to KATU.