As Britain's top-selling newspaper collapses under the weight of its own phone hacking scandal, online activists can take inspiration from their role in the chain of events which brought the News of the World crashing to the ground.

While three days of frenetic online activity bookended nine years of campaigning journalism by The Guardian and tenacious investigation by parliamentarian Tom Watson, Twitter and email were harnessed to strike a vital blow against the newspaper's viability as a commercial proposition - by making it toxic to its biggest-spending advertisers.

As revelations engulfed News International this week, a core of campaigners began to organise themselves on Twitter, questioning corporations' alliances with a newspaper which had hacked the phones of dead soldiers' relatives and a murdered 13 year-old schoolgirl. On Tuesday afternoon, Ford became the first company to publicly distance itself from the Murdoch empire's most influential tabloid. This initial trickle would soon become a flood.

Media journalists were joined by online activists in pressing dozens of companies for statements as to their future commercial arrangements with the paper. But it was bloggers who maintained the most comprehensive and up-to-date records of a rapidly shifting picture - allowing consumers themselves to shame leading brands into pulling the plug.

Within a matter of hours, activists had hacked together a toolkit to lobby companies, publishing the contact details for CEOs with suggested wordings for emails, while easy-tweet buttons harnessed the Twitter API to message official brand accounts. The pressure soon took its toll, with U-turns from the Co-operative group and Virgin Media accompanied by more subtle backtracking from other firms. Health and beauty group Boots, who had confidently told my blog that they would "absolutely" be advertising in NOTW, then insisted that they were "listening to their customers".

On Thursday, with advertisers leaving in droves, Liberal Conspiracy and Political Scrapbook brought a relentless focus to the paper's ten biggest-spending advertisers, accounting for some £12.7 million in revenues. A highly targeted Twitter campaign asked the loyal brands why they worked with an organisation that "hacked dead soldiers' families". With each message providing a link to our campaign tool, a viral feedback effect was created with each firm besieged by hundreds of complaints.

We had planned to perform the same trick late on Saturday night as the paper hit newsstands. Scrutiny of an early edition in combination with an advertising rate card would reveal what the stubborn cohort of remaining advertisers had paid to the paper. Tesco, British Gas and Mars would be asked, in 140 characters or less, what those families hacked after London's 7/7 terrorist atrocities would think of their generosity to the company which eavesdropped on their answerphones.

We didn't need to. At 4:15pm yesterday, news broke that all commercial advertising had been pulled. Thirty minutes later, 168 years of publishing history was brought to a close.

While investigative journalism brought phone hacking to the floor of the House of Commons (and in the future to courtrooms) it was a popular campaign which finished the News of the World as a profitable enterprise. Even Murdoch stablemate The Times, whose loss-making operation was, ironically enough, subsidised by revenues from NOTW, conceded today that the "catastrophic collapse in adverts was driven by online protesters".

The attentions of online activists will likely now shift to the campaign against Murdoch's proposed takeover of broadcaster BSkyB spearheaded by progressive group 38 Degrees. Their fearsome email list, numbering some 750,000 members, has already seen a government U-turns on the sale of publicly-owned British forests. Their response to the consultation on the takeover, delivered this morning, took the form of a 110,000-signature petition.

Trailing some way behind our Atlantic cousins in matters digital, the campaign against News Corporation's phone hacking - and its grab for BSkyB - may yet be remembered as the point grassroots web activism came of age in the UK.

Follow Laurence Durnan on Twitter: www.twitter.com/LaurenceDurnan