The agents, from the Crimes Against Children Squad, will seek to interview the woman, the official said, and try to obtain the text messages and any other evidence she may have in her possession. If they find her account credible, they will take other investigative steps, which could include subpoenaing both her cellphone records and those of Adams from their service providers, the official said.

Federal law bars the sexual exploitation of children under 18, defining a violator as anyone who “persuades, induces, entices or coerces any minor to engage in” a visual depiction of sexually explicit conduct. Several legal experts said that decisions on whether to prosecute such cases could hinge on whether the adult reasonably believed the minor was of legal age, taking into account context from their conversations.

While the inquiry was in its earliest stages, the official said that generally in such cases, agents seek to interview a victim’s friends and family members to determine whether they made contemporaneous statements about the contact.

[Ryan Adams’s album release has been canceled amid an F.B.I. inquiry.]

A lawyer for the woman, now 20, declined to comment as her family deliberated how to proceed. The Times identified the woman by her middle name, Ava, because she was a minor during these interactions. An F.B.I. spokeswoman, Amy J. Thoreson, declined to comment Thursday when asked about the matter.

The Times reviewed extensive communication between Adams and Ava, including direct messages on Twitter that began when she was 14, and more than 3,000 text messages spanning a nine-month period when Ava was 15 and 16. The text messages from late 2014, when Ava was 16, included explicit photographs of her. She said the pair also conducted video calls on Skype, where Adams exposed himself during phone sex. The Times has reviewed screenshots of these interactions.