Six years after Austin Tice, a journalist and Marine veteran, was abducted while reporting on the war in Syria, his parents expressed confidence on Tuesday that he was alive.

The parents, Marc and Debra Tice, spent the anniversary of Mr. Tice’s disappearance publicizing efforts to free their son, 37, who they believe remains a captive somewhere in Syria, entangled in the war.

“It seems like, in many ways, the time has gone so quickly, but we know that, for Austin, it must be grinding on,” his mother said in an interview on NBC’s “Today.” Asked what keeps them optimistic, his father said, “Well, we know he’s alive, and we’re sure he wants to come home.”

They also released a video about his abduction, “Now Is the Time to Free Austin Tice,” which emphasized the historic events over the past six years that their son had missed.