Another said: "F*** me mate, did you not hear the ref??!! We lost thanks to you, you utter urchin!"
A third tagged him on Twitter and wrote: "@SanjayWills single handedly just lost us the grand slam take a f***ing look at yourself for doing something so unnecessary."
WRU has criticised the abuse by taking to Twitter and said fans had crossed the line.
The union tweeted several screenshots sent to Williams and added: "The players are proud to represent their country and their jersey. The abuse players are receiving has to stop. This is a tiny example of the abuse just one player received last night.
"In order to help drive the call for change, the players want to highlight the amount of abuse and bile that circulates on social media platforms. We value our fans 'support in the matter."
Williams and No 8 Taulupe Faletau were both shown a yellow card by ref Luke Pearce which subsequently ignited the fans' anger.
However, the WRU believes this was no reason for fans to act the way they did and Sunday's opponents agree.
France replied through their Twitter account: "All our support dear friends … This is not the true spirit of sport and this has to stop. Congratulations again on the great performance of your team yesterday."
Williams was shown a strong backing by fans following the abuse but hasn't yet commented on the situation.