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.
He has come to symbolize the lethal hazards for news workers covering the war in Syria, where dozens have been abducted. At least five other journalists remain missing in Syria and 122 have been killed since the conflict began in 2011, according to the Committee to Protect Journalists, an advocacy group.
Mr. Tice was attending Georgetown Law School in 2012 when he decided to go to Syria as a freelance journalist to report on the war through its impact on ordinary Syrians, filing articles for McClatchy, The Washington Post and other news organizations. He was detained at a checkpoint on Aug. 14, 2012, near Damascus, days before he planned to depart the country.
Five weeks later, a video emerged showing Mr. Tice blindfolded and held by unidentified armed men. There was no message except the title, “Austin Tice Still Alive.”
His parents have become outspoken advocates for him and other Americans seized abroad and have visited Syria to press for Mr. Tice’s release. They did not say why they believed he had survived after six years. It remains unclear precisely who abducted Mr. Tice or what their demands have been.
But there have been indications that American officials believe Mr. Tice remains in Syria, possibly in the custody of a group aligned with the government of President Bashar al-Assad.
Those indications came to light more than a year ago, in the early days of the Trump administration, when national security officials sought to establish a back channel with Mr. Assad’s government to explore ways to free Mr. Tice.
That contact was extraordinarily delicate because the United States also has sought to ostracize Mr. Assad and has accused his government of atrocities in the war.
The back channel effort appeared to fizzle after a chemical weapons attack in northern Syria in April 2017. Blaming Mr. Assad, President Trump ordered a missile strike on a Syrian air base in retaliation.
A new sign of optimism that Mr. Tice was alive emerged in April, when the F.B.I. posted a $1 million reward for information leading directly to his “safe location, recovery and return.”
Despite no clear sign of progress in resolving Mr. Tice’s ordeal, his parents expressed gratitude to Mr. Trump for what they viewed as his determination to free their son and other Americans seized overseas.
They pointed to the administration’s successful efforts to secure the release of Americans held in Venezuela, North Korea and Egypt.
“For us, this administration is really gung-ho,” Ms. Tice said.