Person of Interest Named in Case of Missing Student Sudiksha Konanki

The desperate search for missing University of Pittsburgh student Sudiksha Konanki in the Dominican Republic is ongoing -- and now, authorities in Virginia have zeroed-in on a person of interest.

Loudoun County Sheriff’s Office spokesperson Thomas Julia confirmed to TMZ that 24-year-old Joshua Riibe is a "person of interest" in Konanki’s disappearance -- surveillance video shows him as the last person seen with her before she disappeared.

We're told Riibe -- a former high school wrestler -- has been "interviewed at length," but Julia emphasized that, for now, this remains a missing-person case, not a criminal one.

As of now, Riibe has not been accused of any crime in connection to Sudiksha’s disappearance during her spring break trip to a hotel in Punta Cana.

Konanki -- a resident of Loudoun County, Virginia -- and Riibe were recorded on surveillance video walking with friends toward the beach around 4:15 AM Thursday, March 6 ... before she vanished around 4:50 AM, according to investigators.

Riibe is reportedly cooperating with authorities -- he claims he and Sudiksha went for a swim but were caught by a large wave. He told authorities he felt sick, but he managed to make it back to shore and fell asleep ... but Sudiksha was never seen again. Previous reports indicated she may have drowned.