First check the appointment letter conditions of termination of job. What are the notice period etc.
If those employees are confirmed / permanent and are absent without any intimation then you should to send letter at their residential address regarding their absence from the office without intimation and action to be action in case of no resonse within 15 days.
Its a accepted form that we should send 3 such letters through registered post with AD.
If there is no response to such letters , you can officially terminate the job of such employees.