Lady Gaga. SV Angel investor Ron Conway. Peter Chernin. MC Hammer. Buzzfeed's Jonah Peretti. Hilary Rosen. Martha Stewart. Arianna Huffington. Goldie Hawn. Lynne and Marc Benioff of Salesforce.com. Suze Orman. Alan Patricof. John Cusack. Esther Dyson. Michael Eisner, Foursquare Co-founder and CEO Dennis Crowley. Frank Quattrone.

What these and dozens of other big-name doers have in common is that they unveiled their support Wednesday for additional federal gun control legislation and stepped up enforcement of existing laws in the wake of the Sandy Hook Elementary School shootings in Newtown, Mass. The list of supporters behind this advocacy effort includes many of the celebrity activists — such as Conway, Union Square Ventures' Fred Wilson and MC Hammer — who got involved in the protests earlier this year against the copyright-related SOPA/PIPA bills.

The group took out a full-page ad in the Wednesday edition of the New York Times, and is embarking on a sustained social-media campaign through Mayors Against Gun Violence's online campaign Demand a Plan. The group is pushing its support for Mayors Against Gun Violence's legislative and action agenda to clamp down on gun violence. New York City Mayor Michael Bloomberg has been acting as a de-facto leader and spokesman for the coalition, which ramped up the campaign Wednesday by asking the public to sign a petition aimed at the President and members of Congress. Bloomberg, known as a techophile himself, launched a new project Tuesday that released videos of 34 Americans who have been affected by gun violence, and who are calling on federal lawmakers to take action.

The tech industry's use of the Web as a bully pulpit could prove interesting, if they decide to use it in the face of expected Republican opposition to the measures from the House.

Mayors Against Illegal Guns wants Congress to enact a law to close a loophole that lets "private" sellers of guns evade the process of conducting background checks on people who buy guns. It estimates that 40 percent of all gun sales in the United States occur without any background checks on buyers. Some members of the coalition also want to ban military-style assault weapons, and make gun trafficking a felony, among other things. A full list of their agenda is here.

Wilson first blogged about his support for the campaign on Wednesday morning.

"Like the PIPA/SOPA efforts last year, this effort is diverse, distributed, chaotic, and hopefully effective and powerful," he wrote. "I am not aware of everything that is going on right now. There is a lot of activity out there. But I will try to stay on top of it today and keep you all up to date as well."

PIPA/SOPA refers to the pair of copyright-related bills that the startup community defeated in a high-profile push early this year. Some of the most high-traffic sites on the Web, including Reddit and Wikipedia, blacked themselves out for the day to protest the proposed legislation. (Wikipedia Founder Jimmy Wales' name isn't on the Who's Who list of people supporting Demand A Plan, but he did tweet out a link to the site Wednesday.)

While a SOPA-scale campaign across the Web on gun violence sounds intriguing, there's already support at the top for most of what the coalition is asking for. President Obama addressed many of the group's points in a press conference Wednesday morning.

"The good news is there’s already a growing consensus for us to build from," he told reporters. "A majority of Americans support banning the sale of military-style assault weapons. A majority of Americans support banning the sale of high-capacity ammunition clips. A majority of Americans support laws requiring background checks before all gun purchases, so that criminals can’t take advantage of legal loopholes to buy a gun from somebody who won’t take the responsibility of doing a background check at all."

He added: "I urge the new Congress to hold votes on these measures next year in a timely manner. And considering Congress hasn’t confirmed a director of the Bureau of Alcohol, Tobacco, and Firearms in six years -- the agency that works most closely with state and local law enforcement to keep illegal guns out of the hands of criminals -- I’d suggest that they make this a priority early in the year."

All those measures also have a key ally in the Senate in the form of Sen. Diane Feinstein of California. Feinstein, a Democratic, has vowed to support a renewal of a lapsed ban on military-style assault weapons. That's key because Feinstein is expected to become chairman of the powerful Senate Judiciary Committee next year.

Both Bloomberg and Boston Mayor Thomas Menino thanked the coalition for its support Wednesday.

"This ad speaks for the millions of people across America who refuse to remain silent any longer as their friends, neighbors, and loved ones fall victim to gun violence," Menino said in a press statement. "These people are doing their part to spur meaningful action on the issue – the President and Congress must follow suit. Without any action, 12,000 people will be murdered with guns next year alone. That is simply a price Americans are not willing to pay.”