Here's the main thread:
http://www.chess.com/forum/view/livechess/new-logic-for-auto-pairing-and-seek-graph
And here's the new article in Help & Support:
https://support.chess.com/customer/portal/articles/1622811-how-are-seeks-matched-in-live-chess-
And finally, You can still set rating range manually (including unrated) by selecting Custom in the time control menu; a rating option button will pop up that you can press.
When playing live chess, you could set the minimum-maximum rating for the opponent you wish to play. It is now gone, so how do you play against similar rated players?