Williams' message was retweeted 1342 times, favourited by almost 1900 of his followers and his Twitter feed was flooded by messages of support.
Former golf world No 1 Greg Norman was among those who backed Williams' gesture, tweeting: "Love to read and see this. Well done. A credit to your country and #RugbyWorldCup."
Kiwi technology commentator Peter Griffin said a combination of the personal touch from players and an official social media campaign from New Zealand Rugby which wasn't bogged down by corporate-speak had ensured the All Blacks had triumphed in the Social Media World Cup.
"The level of instant reaction from fans to on and off-field events is a community culture we never saw a few years ago," he said.
"The All Blacks' campaign has been clever by not being overtly corporate. If just a small percentage of social media followers convert into merchandising sales this could be lucrative."
Griffin added of Williams' tweet: "[It] was a PR masterstroke and will have done his personal brand no harm."
The likes of Twitter, Facebook and Instagram were around for the 2011 Rugby World Cup, but they hadn't been embraced to the same level by our leading players and fans.
Four years on, big-name performers like Williams and Daniel Carter boast almost half a million followers each on Twitter. And many of their posts have been retweeted thousands of times.
The All Blacks' official Twitter account has a whopping 542,000 followers. Their opponents in this morning's final, the Wallabies, have just 170,000.
World Rugby's official Rugby World Cup Twitter account has 656,000 followers.
Throughout the campaign, we have been given a rare insight into the off-field antics of the All Blacks and their partners in the UK.
Griffin said players had been well trained on the power of social media. None of the men in black fell foul of posting the types of howlers that have dogged the Wallabies over the past few seasons.
Griffin said one of the other masterstrokes of the All Blacks' social media blitz was the involvement of some of the partners.
That includes Gemma Flynn, the partner of captain Richie McCaw, who has tweeted pictures of herself with her famous beau and visiting the London Eye with family.
Caroline McNaught, partner of All Blacks' back-up centre Malakai Fekitoa, was seen getting up close and personal with a waxworks model of Hollywood heart-throb George Clooney at Madame Tussauds.
The wife of blockbusting wing Julian Savea, Fatima Antaqi-Savea, posted on Wednesday a pic of her and her star hubby on a shopping expedition in London, with the message: "Had a fun day out in London with this lovely man of mine".
She then followed it up with the tweet: "No one can ever say us partners are a distraction to our men when we only get to see them for a couple of hours once a week on their day off."
Griffin said the posts featuring partners showed the players' "human side".
That included pictures of Victor Vito, his wife Amber Vito and their 10-month-old son Karlos.
"The players and their marketing advisers are well aware of this and they are taking full advantage at this world cup."
