Some months ago I made a tool for this exact purpose.
You can filter your library or wishlist by any combination of one or more tags and features, and also sort by your playtime or Metascore.
You're welcome :) http://www.lorenzostanco.com/lab/steam/
gaming.stackexchange.com/users/101551/lorenzo-s
You can filter games in your library using certain features by using Enhanced Steam (browser plugin for FF and Chrome).
You'll need to install the plugin to your browser, go to Steam website and enter the settings from the new Enhanced Steam dropdown.
Then enable Library (BETA, only available in Chrome), if it's not already enabled and go back to Steam's website.
You should see a link to your library at the top of the page.
Click it and you can easily filter your library: Categories include the features you can see on the right on Store pages such as VR-support, local co-op, multiplayer and controller support.
Genres include, well, genres.
The best way to search for games with tags is by going to the tag page ( http://store.steampowered.com/tag/<language>/<tag>/ where language is the shortcode for a country such as "en" for English or "fi" for Finnish) and browsing for games you own (Enhanced Steam can help you highlight those as well).
You can further filter those results by using the filters on the right.
gaming.stackexchange.com/users/51318/3ventic
Since the "Discovery" update a few days ago, the Steam store now marks games that are in your library on various search and store pages.
Here's me searching for the co-op and fps tags: The ones that are dimmed and have the 3 bar icon are games I already own.
Note: I'm using common tags to demonstrate how it works, you can search by less common tags using the search box.
However, the library itself has not been changed to search by tag.
gaming.stackexchange.com/users/87105/Powerlord
This tool lets you filter your games by Singleplayer, Multiplayer, Co-op, Local co-op, Controller, Mac, and/or Linux.
It can also let you filter an intersection of games between different accounts.
gaming.stackexchange.com/users/71646/radomaj
There is currently no way to filter the Steam Library by Steam Community tags or feature lists.
You can, however, apply a single category to every game through the context menu of the item in the library.
Your games then get grouped by category.
gaming.stackexchange.com/users/41081/user98085
I found a tool that requires a little more work than the web-based ones above, but has an amazing amount of functionality.
Depressurizer will parse your Steam library and load it into the application for query and edit.
You can sort / filter games by categories, tags, all sorts of stuff.
You can automatically apply bulk label operations based on certain conditions, etc, then sync your changes back to your library.
If you just want simple search, use one of the web-based ones in the other high-ranked answers.
If you want powerful tag/category modification tools then definitely try Depressurizer.
gaming.stackexchange.com/users/17522/James B
Shameless plug, you can use my site to filter your single-player games by genre, metacritic score, and release year: https://www.howlongtobeatsteam.com .
Just go to the table at the bottom and click "Advanced Filter".
You can then sort the results by playtime if you're so inclined.
gaming.stackexchange.com/users/66943/Ohad Schneider
I can look through the "Store" portion of Steam using tags, and I can also do an advanced-search on certain features like local co-op support.  But for some reason, when I do this I can't tell which games I already own, and I don't seem to be able to do the same search / filter when viewing my library.  Am I missing an option somewhere?  It seems like a no-brainer to be allowed to do this.
Can I filter my Steam library by tags or features?
gaming.stackexchange.com
<steam>
gaming.stackexchange.com/questions/159350
gaming.stackexchange.com/users/17522/James B
You can filter games in your library using certain features by using  Enhanced Steam  (browser plugin for FF and Chrome). However, there is currently no way to filter the Steam Library by Steam Community tags or feature lists.   While it seems impossible to sort Steam library by tags or features, there is an option to manually tag and sort games in library.
A user is implying that plug ins are in need. While someone else is suggesting that there is no way to such a thing. On the other hand, it seems that Steam offers a similar option.