Finding a Missing Relative?

What can I do to find out if my sister's son is still alive? The last time he collected his disability pension from SASSA was at the end of June 2012. We have been trying to locate him through Missing Children, friends, and family. Now, after such a long time, we are not sure if he is dead or alive. We accept the fact that he could be dead, but obviously would like to get closure. Where on the web can I go to find out if he is still alive (or dead)?

By E. de V.