I tend to notice that the players who often get reported claim to say they won't get banned or warned or punished at all. When someone says that they'll report them, the toxic player gets even more toxic, and so far, out of all the notifications I have gotten of my report going through and punishing the toxic player, the ones that have worked were the ones where the toxic player is told that they'll be reported.
I stopped asking others to report a player. I haven't done that since 2012, and I have pretty much just put the player on mute and reported them at the end of the game. I'm glad that I rarely had to do that up until this year, and now, I am pretty disappointed, because it seems that many players (at least in the Bronze to Silver tiers) tend to be extremely toxic.