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May 5, 2015, 7:39 PM GMT / Updated May 7, 2015, 2:50 AM GMT By Tracy Connor

When American soldier Allen Thomas waved goodbye to his twins at an airport in Korea in 1971, he had no idea it would be the last time he would see them.

More than 40 years later, the veteran has turned to social media in an effort to locate his long-lost children, who were put up for adoption after he returned to the United States.

"I just want to see my kids and know that they are okay. I want to let them know I love them," Thomas said.

"I want to share our family health history with them, because some of it is serious. I want them to know that I have never stopped trying to get them."

A Facebook post by Thomas has been shared 1.2 million times in a few days, and an online group set up to generate leads has garnered 25,000 members.

The quest has left Thomas so emotional that he has difficulty even speaking about the situation and asked his adult daughter, Charlene Roberts, to share details of the family history.

"I want the kids to see it and I want them to know he's been looking for them," Roberts told NBC News on Tuesday.

Thomas was just 18 years old when he joined the Army, and he shipped out to Korea the next year. That was where he met a woman who was soon pregnant with twins. A boy named James and a girl named Sandia were born Sept. 10, 1967, and he and their mother married some months later.