If you have troubles with searching in Casual and Ranked, you can try this.
How to Fix Ranked and Casual Search Issue
If you have any trouble in searching for player like: getting players with 300+ ping, “network errors” and stuff or can’t search anyone at all, try this.
In Steam App go to Steam->Settings->Downloads and try to select different Download region for some you think can have a good player base.
It work for me. After i changed “Russia-St. Petersburg” to “France-Paris”, game finally stop sanding me Chinese with 300+ ping and start to find players from EU with good ping.