Toure, 19, started an assessment with Amakhosi earlier this month, along with Italian Gustavo Paez, Brazilian Pedro Henrique Dias DeAmorim and Malawian Miracle Gabeya.
Amakhosi have since announced the defender failed to board a returning flight home after being transported to the airport this week.
Chiefs said on Twitter: 'Ismael Olivier Toure, a trialist at Kaizer Chiefs never boarded the plane to return to Ivory Coast.
'Ismael Olivier Toure, a centre half was released this week and transported to the airport.
'Ismael Olivier Toure, he was transported and checked in at OR Tambo International.
'The player arrived in the country on our invitation and therefore it is our responsibility to ensure his safe return.
'We have notified all the relevant authorities to help establish Toure’s whereabouts.'