Forty years on, babies of the Vietnam war continue to look for their birth parents, often of mixed parentage.

Some like Tricia Houston have successfully used DNA studies and Facebook to find their parents.

"This man looked really sad and like he was searching for someone all his life," Houston told ABC News about a Facebook post.

DNA test results matched the two as father and daughter and Tricia plans to return to Vietnam next month to meet her father for the first time.

Others like Chantal Doecke, adopted by an Australian couple is hopeful of finding her birth parents too. So is Sue Yen Byland from Perth who believes her mother was Vietnamese and father an American veteran.

About 100,000 children are believed to be born from relationships between local women and American soldiers during the conflict.

The war ended with Operation Babylift in 1975 that saw 3,000 infants from orphanages and hospitals flown out of Saigon to nations around the world.

Some of those adoptees return next month to Vietnam to mark the 40th anniversary of the evacuation. Many are on a long quest to find their birth parents.

While in the United States, a DNA database has helped a dozen adoptees finding their birth parents, there was no such database in Australia nor in Vietnam.

Thousands of children were fathered by American soldiers sent to support the South Vietnamese army in the war against the North.

Following evacuation by American troops, the Vietcong set about purging all memory of the two decade-long US intervention. Many Vietnamese women abandoned their children and fled as the Vietcong hunted them down. All birth records were destroyed.

The plight of these children way back in the 80s has been described as pathetic. Found begging for food on the streets, locals treated them cruelly.

Some of the American war veterans now in their 60s and 70s are still looking for their offspring. Some have been lucky, while many seem uninterested in knowing their biological children.