From the All Content are or an individual site you can use the All Articles section to search articles. You can filter articles by tags, owner, status, and more so you can find any article in your knowledge base.
Click on All Articles
Search using the tag: filter
In the Filter by field type
tag: followed by the name of the tag you would like to search for.
If your tag has spaces in it then enclose the tags in quotes. E.g.
Filtering by Owner, Status, and other fields
For all other article properties you can use the provided menu to select the filter critera.