Still, some cases don't end well, even if the missing people are located.

"Some young people couldn't stand the way their parents treated them. Some others refused to return since they hadn't achieved enough to allay fears their families and friends wouldn't respect them."

Sui often uses his free time to search for people.

"He's in his office every time I pass by - even on weekends," says his colleague, Yuan Jiayu.

"He spends a lot of time looking for missing people, even after his workday is done. His efforts are invaluable."

Sui calls this mission an "endless social responsibility".

"I've seen the pain of families with missing loved ones," he says.

"Someone should help them. I'd like to be that someone."

His story has even inspired some members of the public to volunteer to help him search, such as Yu Guomin, who retired from a high school in Hangzhou last year.

"I can visit families and collect information when Sui is busy," Yu says.

Despite his achievements, Sui still has regrets. Sometimes, he couldn't locate the missing people despite his best efforts due to a lack of leads.

"Beyond the 3,500 reunited families are perhaps hundreds of thousands who are still tortured by the fact their loved ones are missing. I will continue to help them."