Yingying Zhang, 26, was about a month into a yearlong appointment at the University of Illinois' Urbana-Champaign campus when she vanished June 9. Her friends told police she had gone out to sign an apartment lease.
Campus police spokesman Patrick Wade said the FBI has labeled the case a kidnapping but isn't ruling out anything.
University police released surveillance video Monday showing Zhang getting off a bus in Urbana the afternoon of June 9 and entering a black Saturn Astra vehicle shortly thereafter. Authorities have asked the public for help identifying that vehicle.
"We have her on video getting into a car and that's the last we see of her. That's obviously very concerning," Wade told The (Champaign) News-Gazette.
He said at least four FBI agents are in Urbana working on the case and helping Illinois State Police sort through tips and other information. Detectives were also examining Zhang's cellphone records and working with ride-hailing companies such as Uber to see if she may have called for a ride.
The FBI plans to post information about Zhang on billboards across Illinois and in the Indianapolis and St. Louis areas through an agreement with an outdoor advertising company, Wade said.
Zhang, who is from Jianyang, China, was working in the University of Illinois' Department of Natural Resources and Environmental Sciences, researching photosynthesis and crop productivity.
Campus spokeswoman Robin Kaler said her appointment as a visiting scholar runs through April 2018.