Hi,
You need to follow the disciplinary process.
Try to reach the employee through alternate options like 1) through email 2) alternate emergency contact number if took at the time of joining.
In case of no response serve warning letter through Registered Post with Acknowledgement Due (RPAD). Warning letter to be dispatched to both personal and permanent address as available in the personal file.
Provide sufficient time frame for the employee to report back. Wait for the RPAD Acknowledgement due. Check whether signed by the employee or others.
Process for termination if the employee fails to report back even sufficient time frame provided.
Keep copy of all communications in the personal file of the employee.