A search is underway for a Chinese student missing in the United States for the last four days. 

26-year-old Zhang Yingying is a visiting scholar at the Department of Natural Resources and Environmental Sciences at the University of Illinois and has been in the US for about a month. 

UIUC Police Department Chief Jeff Christensen said on Tuesday that the police will "do everything" to find her, adding that they have have been offered additional resources from the FBI and other law enforcement agencies.

Zhang Yingying was seen getting off the Teal line bus in surveillance video. /Police handout

According to police, Zhang has not been seen since Friday, after telling friends she was going to sign a lease on an apartment with her agent from One North, a local agency. 

Surveillance video footage showed her entering a black Saturn Astra vehicle at around 14:00 local time, shortly after getting off a bus.

Zhang's friends called the police on Saturday. Her last phone call was made at 14:30 on Friday afternoon, and when her agent contacted her at 14:38, she did not reply. 

Zhang's friends get involved

Zhang's friends and classmates have been seeking help through various methods, including posting notices on Facebook. 

The clothes Zhang was wearing when she was last seen.  /Police handout‍

Her friends have also been trying to decode her Apple ID, in efforts to locate her phone.

News of Zhang's disappearance has gone viral on Chinese social media site Sina Weibo after several Chinese media outlets reported it. 

Earlier information indicated that police had located the black vehicle Zhang was seen getting into but UIUC police spokesperson Patrick Wade denied this, saying that police have been cooperating with ride-sharing companies such as Uber and Lyft. 

A screenshot of Zhang's conversation with her real estate agent.  /Provided by Zhang's friends

Police released photos and information about Zhang to assist in the investigation, and have posted regular updates on their official website.

Chinese consulate intervenes

The Chinese Consulate-General in Chicago initiated an emergency plan on Tuesday. Deputy Consul-General Yu Peng spoke by telephone with UIUC headmaster Robert Jones and police chief Jeff Christensen, to discuss the case. 

Yu conveyed Consul-General Hong Lei's concerns and expressed the hope that police will invest more resources into the search operation. 

The Chinese consulate, Chinese students and the local Chinese communities will provide necessary help to the police, said Yu.

CGTN Photo