To launch a search within Surf, tap on the bottom bar.  Search results include relevant custom feeds, profiles, Flipboard Magazines, YouTube videos, podcasts, RSS feeds, and hashtags.

To use search, select the option and search for the term you would like:
 

The top items will be more specific results, either matching exact terms or items that are generally about the terms and then some related topics.

Tap to view the results feed. The source can be added to a custom feed or shared with others.