(CNN) -- Police in Norwalk, Ohio, are searching for a 17-year-old girl who has been missing since June 7 after trading text messages with her boyfriend that indicated the two were planning to run away together, police Sgt. Jim Fulton said Monday.
Fulton said police believe Abbi Obermiller left her grandparents' home on her own accord late on the night of June 6, but said detectives are "concerned" that the situation may have changed and that there is a "possibility she is in danger."
He declined to elaborate on what information authorities have received that led them to believe her situation possibly changed.
Investigators in the case have uncovered a series of text messages between Obermiller and her boyfriend, identified by police and by Obermiller's parents as 20-year-old Robert Young of Norwalk, that appear to be coordinating when she would be picked up from her grandparents' home in the early morning hours of June 7, Fulton said.
According to Fulton, Obermiller repeatedly sent messages to Young asking, "How much longer?"
At 12:45 a.m. June 7, Young responded and told her to "leave now," Fulton said.
The last text message from Obermiller appeared to direct Young to her location, Fulton said.
CNN could not immediately reach Young for comment Monday night.
Young has denied knowledge of Obermiller's whereabouts, according to police.
Young has told police the messages were a week old and were sent over Memorial Day weekend while the couple coordinated a swimming date, Fulton said.
However, other evidence indicates the couple were making plans to run away after Obermiller's parents expressed disapproval of their relationship, Fulton said.
Young was charged June 14 with obstruction of justice in the case for his failure to cooperate in the investigation, authorities said.
A text message to one of Obermiller's friends sent before her disappearance indicates Obermiller knew she would be going away.
In it, she tells her "bestest friend" that she won't be able to talk for a while so "don't forget me," according to Fulton.
And a note found in her grandparents' home reads: "I just couldn't take any more of this drama, it's not good for me. Love you all. Hope to see you soon. Love, Abbi," according to Fulton.
Fulton also said one of Obermiller's friends told police she saw Abbi wearing a wedding ring.
"We do believe that Bobby does know where she's at, he just doesn't want to tell us," Obermiller's mother, Rose Obermiller, told HLN's "Prime News" on Monday night.
Rose Obermiller told "Prime News" that she initially approved of her daughter's relationship with Young, but that Young's behavior grew increasingly alarming.
"In the beginning he was a nice Christian boy," Obermiller said. "He went to church, he was on the baseball team, he was on the basketball team (and) he really cared for Abbi.
"But as it went on, he was telling her, 'No I don't want you to be class treasurer; no, I don't want you to go to New York with your choir; no, I don't want you to see these friends and relatives," Obermiller said. "He was telling her what not to do."
Fulton said Young has declined to take a polygraph test in the case.