We all have the same problem, how to find inactive players in our friends list. There is a website: http://www.forge-db.com/. This site provides what you are looking for to remove inactive friends.
Once at the site, place your mouse on 'Servers' and click the country's server you are needing. this will give you a list of worlds for the country you selected.
Next click the world your are needing to manage your inactive players in your friends list. You will get some statistics for the world you selected.
Now click Players. You now get a list of players in the world you selected. In the search field type the name of the player you are wanting to check their activity. You do not need to press enter, the web app will start searching when you type in the players name. You will get a list of players or just the player you are looking for, if the player doesn't show, check the spelling in the search field.
If the players name has a red/pink background, that means the player has not been active for at least 24 hours, if a white background shows, the player has been active in the last 24 hours. If the player has a red/pink background, right-click the player and from the dropdown, choose 'Open in a new tab' or 'Open in new window'.
When the new tab/window has opened (this may take a few seconds) click on it and you will see some statistics about the player. Scroll down and you will see some graphs showing 'Points' and 'Battles'. If you see the graph. Here you can see the last activity the player has had over the last year and you can see if the player is no longer participating in the game by earning points and/or participating in battles.
No activity? Delete from friends list.
ALTERNATIVELY a method that I have found that works great-PC
when friend list reaches 135-140 the following late thursday or early friday I aid evveryone like usual.
no more aid until late sunday night. town hall, event news, filter for friends and social events.
aid back until you hit thursday.
go to friends list. Any that still need aid, get one last, checked for a snipe, and given the boot.
Since people are typically more qctive on the weekends this gives everyone the best chance to NOT be kicked for inactivity.