1.Go to Following Navigation.  PeopleTools>portal>General Settings

2.Check the DISPLAY SEARCH IN NAVIGATION BAR  and DISPLAY SEARCH  IN HEADER. And Save it.

3.Go to Following Navigation.  PeopleTools>portal>Build Registry Search Index

4.Run the process by choosing any run control Id.

5.Go to process monitor.

6.Check if process completed successfully.

7.Restart the PIA

NOTE: It was tested on people tool version 8.49 and 8.50