The Bulls said that Nkosi, who has played 16 tests for South Africa and was part of the squad that won the 2019 Rugby World Cup, has been "absent without leave" for three weeks.
"Nkosi's last known contact with any executive, management or playing squad member is Friday, Nov. 11, 2022," the Bulls said in a statement on Saturday.
"After numerous failed attempts, which include but are not limited to phone calls, texts messages, calls to relatives, partner and close friends as well as four house visits to his known place of residence, the company took the decision to open a missing person case.
"This resulted from the grave worry and concern of everyone at Loftus as well as the need for the expert assistance of the South African Police Services."
Nkosi was named in South Africa's squad for their tests against Ireland, France, Italy and England in November, but was ruled out of the autumn internationals after suffering a rib injury while playing for the Bulls in the United Rugby Championship.
