Its Union Square headquarters are now shuttered and its army of dedicated cotton-tailed do-gooders is long gone. But a group of activists who invaded Union Square for two weekends last month urging passers-by to sign petitions has vowed to keep fighting.

The college-age activists claim they are fighting to get June 1 declared ‘Lactose Tolerance Day.’ They are nothing but the latest example of what has come to be known as viral marketing.

Their campaign began in August with a demonstration at the MTV Video Music Awards. Dozens of young people marched outside Radio City Music Hall waving placards proclaiming “I love chocolate milk.” From its street-level headquarters, the movement’s volunteers asked passers-by for support, much like Greenpeace and Amnesty International do (except that they were dressed like rabbits). They handed out buttons, T-shirts, and a “lactose tolerance kit” complete with free Nestlé chocolate milk.

This was not a political campaign, but part of an on-going marketing campaign orchestrated by Nestlé for its Nesquik flavored milk mixes.

This is not the first time a company has used the streets of New York to promote its products — Microsoft landed in hot water with city officials when it posted thousands of adhesive butterflies on traffic poles in 2002 to promote its MSN 8 Internet service.

Nestle’s latest campaign is part of a rising trend in viral marketing. Kevin Lane Keller, a marketing professor at Dartmouth College, says “viral” refers to the use of blogs and Web sites to get corporate messages across. Throw in experiential marketing (mock protests) and you have a particularly effective way to reach younger audiences.

“Viral marketing has become more common as traditional ways of marketing are seen as less effective. It’s a real challenge to break through to this audience,” Mr. Keller said.

Nestlé built a Web site for lactose tolerance complete with its own blog and inauthentic postings. Nestlé has also produced faux public service announcements, posted on YouTube, that parody sanctimonious television advertisements enjoining people to support the cause. “Practice lactose tolerance and make the world a better place,” pleads one woman on screen.

Nestlé is pretending this campaign is for real, with the Lactose Tolerance group claiming to be a grassroots movement. The activists all stayed in character during the street recruitment drive. Even the Cleveland-based advertising agency behind the campaign, Marcus Thomas, wouldn’t budge. “We wanted to spread the love for milk, and tolerance for all things,” said Michelle Vocaire, the campaign manager, not deviating from the script.

Ms. Vocaire conceded that the campaign, the first Marcus Thomas has done for Nestlé, was designed to be “something quirky and fun in a very serious political campaign season.”

Alhough Mr. Keller said this spoof is innocuous and doesn’t cross any lines, his concern is the campaign’s effectiveness in building Nesquik’s brand. “It’s surprising they haven’t tied it into Nesquik yet. It’s too indirect,” he said.

What’s more, the campaign has confused some into believing it supports lactose relief pills and makes light of a health problem that afflicts some 30 million Americans.