One of them, identified only as "Ava", showed reporters more than 3000 explicit texts she said she exchanged with the star when she was 15 and 16.
His lawyer has rejected her claims.
"Mr Adams unequivocally denies that he ever engaged in inappropriate online sexual communications with someone he knew was underage," Andrew B Brettler told the New York Times when the story broke on Wednesday.
An unnamed FBI source later told the newspaper it was looking into the allegations, and would seek to interview the woman, who is now 20, before deciding how to proceed.
The original New York Times story contained interviews with several women who said Adams had offered them help with their careers as a pretext for sex.
Model and singer-songwriter Karen Elson also shared a post about her experience with Adams.
Ryan Adams accused of sexual misconduct by several women
New York Times
Several women have accused the singer of emotional and verbal abuse and of offering career opportunities as a pretext for sex.
A New York Times report outlines a pattern of manipulative behaviour, including accusations of psychological abuse from his ex-wife, Mandy Moore.
Ryan has denied the allegations.
"But the picture that this article paints is upsettingly inaccurate. Some of its details are misrepresented; some are exaggerated; some are outright false. I would never have inappropriate interactions with someone I thought was underage. Period."