Four Vietnamese exchange students who vanished more than 18 months ago while staying with South Australian host families have still not been found.

Sunnie Nguyen, then 17, was discovered missing from her room after having dinner with her host family at their South Plympton home, in Adelaide’s inner-south, on January 8, 2024.

Several personal belongings — including the Year 11 student’s backpack, laptop, ID documents, and some clothes — were also gone and her phone was switched off and social media accounts wiped.

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As Sunnie’s host mother May Zervaas made a public appeal for help to find her, it was revealed three other international students were reported missing between December 2023 and January 2024.

SA Police are yet to locate the four teenagers, who they believe are “actively avoiding authorities”, a spokesperson confirmed to www.20304050.best this week.

“There is no information or evidence uncovered to date which would indicate these youths are in immediate danger,” the spokesperson said.

“SA Police are working with other agencies to help locate these youths and ensure their welfare.

“Contact has been made with the families of the youths in Vietnam, during this contact families have not shared any concerns for the student’s welfare.“

The four students are believed to have been attending Hamilton College when they disappeared.

They each went missing at separate times and it is understood police are investigating whether they travelled interstate.

Sunnie had appeared to be happy and had no reason to run away or hide as her visa was still active for another three years, Zervaas told 7NEWS at the time.

Anyone with information is urged to contact SA Police on 131 444 using report number 2400009568.