'NCIS' Actor Adam Croasdell Allegedly Catfished and Harassed Online

Adam Croasdell -- an actor known for his roles on "Preacher," "Reign" and "NCIS" -- has gone to the cops, claiming he'd been catfished by someone who is now mercilessly harassing him online.

According to new legal docs ... Adam says he began communicating with the owner of the IG account @topthatpose in April 2017, and the 2 eventually exchanged digits and began talking daily.

Adam says the person claimed she was a 24-year-old woman named Gabriella Winters, and they developed a relationship ... but "Gabriella" would always find an excuse to avoid meeting with him ... even on FaceTime.

According to the docs ... Adam broke things off in July 2017, but he began getting bombarded with harassing emails and social media messages shortly thereafter. He claims he was getting 10-50 messages a day from "Gabriella" through hundreds of different accounts.

Adam says the catfisher even pretended to be various members of Gabriella's family.