I have implemented them in one of lightning component. I used forceCommunity:themeLayout interface and able to customize my pages in Napili template, but i didn't find any code on how to use the profileMenuInterface and searchInterface.
Profile and Search interface represents the header search and profile components.
To use it, you should go to Community Builder-> Settings -> Theme and check
* Use a custom search component
* Use a custom user profile component
And select the custom components you already created implementing those interfaces