Greg and Cathy Crowell of Canada, with their adopted child Hosanna.[Photo provided to China Daily]

In the past decade, Hosanna, who will celebrate her 11th birthday this spring, has been living in Alberta, Canada, with the couple. They have returned to the welfare house during that time, but have had no luck in finding her biological parents.

Doctors in China and Canada have told the couple that the only way to cure Hosanna is through a bone-marrow transplant, which requires a match that is most likely to be found in a sibling.

The couple recently posted an open letter online, announcing the search for relatives of the girl. They offered to cover the cost of blood tests to find a match "because these people could possibly help Hosanna in a physical way that we will never be able to", Cathy Crowell said.

The letter caught the attention of the authorities in Tianzhu, who have pledged to assist the couple in their search.

Led by the local internet information office, a notice was made to spread Hosanna's story in the hope of tracking down a relative. Copies of the notice were given out to local school heads, who were told to pass them on to students and parents.

While there have been no leads so far, the couple said they remain hopeful.

"We do not want to pressure them. They need our respect and we want them to come forward on their own. This is not easy for them," Cathy Crowell said.

Nevertheless, the couple have been introducing Hosanna to Chinese culture and she has been learning Mandarin for five years.

"We hope that one day she can help us visit China and be our interpreter," Cathy Crowell said.