The father of missing visiting Chinese scholar Zhang Yingying read a letter the family sent to US President Donald Trump, asking him to "direct all federal resources to try to find Yingying," on Tuesday at a news conference in Champaign, Illinois.

Zhang Ronggao was joined by Zhang's mother, Ye Lifeng, and younger brother, Zhang Xinyang.

The family said they hope their appeal to the president will advance the search for Zhang. They also said they will not give up until Zhang is found.