Sometimes, the exhausted father has no money in his pocket and has to go hungry or sleep rough.

Occasionally, he is reduced to tears when "chengguan" (urban management officers) force him to tear down the notices he has posted on the street.

However, kindness has supported and comforted him along the way.

To save time, Guo once rode his motorbike on a motorway, which is not allowed. After traffic police saw his flag, they did not fine him or force him to leave, but escorted him until he reached his next stop.

An officer even wrote him a note, wishing him luck in his search.

"So many people have helped me over the years. Though I don't know their names, I know I'm not alone on the road," Guo said.

His wife has given birth to another two boys since the abduction. But the family has never taken a photo together. "I want to wait for my lost son and be a complete family again," he explained.

Guo said he feels sorry for the sons he has left behind but he can't stop his search because it has become about more than his family.

An estimated 1.2 million children worldwide are trafficked every year, according to the International Labor Organization.

While looking for his own son amid the murky world of human trafficking, Guo has found lost children for several other families. He carries around a collection of missing-person notices.

Now he wants to do more, having established an association to help those with similar experiences.

"If there is a platform through which people who've lost children or who were abducted during childhood can exchange information, the road ahead can be less lonely," he believes.

"As long as there's a ray of hope, I won't give up," said Guo. "My son's name is Guo Zhen. He was born in April 1995. There's a scar on the little toe of his left foot."

As soon as the festival ceremony was over, he set off once more on his motorbike. "Where are you, my son? Daddy will take you home" receded into the distance.