The advocacy group started by President Obama’s former campaign officials began its first advertising campaign Friday, pressuring 13 Republican members of Congress in their home states to expand background checks to all gun buyers.

The ads, which include the legislators’ photos and Twitter handles, are running on local-news Web sites in lawmakers’ home districts. The ads, which officials said cost close to $100,000, represent the first paid media campaign by Organizing for Action (OFA), the nonprofit group formed last month to harness Obama’s campaign apparatus in support of his legislative agenda.

The ad buys come as Obama and Vice President Biden apply pressure on Congress to vote on the administration’s gun-control agenda, which includes universal background checks as well as bans on assault weapons and high-capacity magazines.

On Friday, OFA also held its first “day of action,” staging more than 100 events across the country. The events included house parties to write letters to the media and Congress, rallies featuring local surrogates such as police chiefs and mayors, and candlelight vigils to remember people who have been killed in shootings.

The events were focused on background checks, the most popular of Obama’s gun-control proposals. With Congress members still at home for recess, OFA officials hope the events and online ads will help demonstrate grass-roots support for toughening background-check requirements. Senators could take up the background-check proposal next week when they return to Washington.

How the NRA exerts influence over Congress

“We decided to focus on background-check loopholes today,” OFA spokeswoman Katie Hogan said. “It’s not that we don’t support the entire plan to curb gun violence; we do. But since there’s such a broad consensus about background checks, we thought it was important for us on our first ‘day of action’ to push members of Congress who have yet to take a stance.”

OFA’s ad campaign does not target Republicans who already have voiced support for expanding federal background checks, such as Sens. Mark Kirk (Ill.) and Tom Coburn (Okla.).

Instead, the ads are aimed at 13 Republicans whom OFA officials believe could be swayed to support the proposal but have not yet stated a position. The lawmakers hail from states Obama carried in his reelection last year, including California, Minnesota, Pennsylvania and New Hampshire.

The targeted lawmakers are Sens. Kelly Ayotte (N.H.) and Susan Collins (Maine) and Reps. Mike Coffman (Colo.), Jeff Denham (Calif.), Jim Gerlach (Pa.), David Joyce (Ohio), John Kline (Minn.), Howard P. “Buck” McKeon (Calif.), Gary G. Miller (Calif.), Robert Pittenger (N.C.), David Valadao (Calif.), Daniel Webster (Fla.) and C.W. Bill Young (Fla.).

The ad campaign was first reported by USA Today.

Other OFA efforts on Friday were aimed at additional lawmakers. Jon Carson, the group’s executive director, e-mailed Obama supporters urging them to tweet or call their members of Congress. The e-mails are personalized by congressional district and include the Twitter handles and phone numbers of the recipient’s local representative.

“If Congress passes legislation requiring universal background checks — which are supported by 92 percent of Americans and even 74 percent of NRA members — it will be an important step toward keeping our kids and communities safer from gun violence,” Carson wrote in the e-mails. “But it won’t happen unless we demand it. . . . With just a couple clicks, you and many other constituents will create a drumbeat that can’t be ignored.”

Discuss this topic and other political issues in the Post’s Politics Discussion Forums.