A forum on how social media can benefit small businesses is a featured event at National Small Business Week, now underway in Washington, D.C. But perhaps the U.S. Small Business Association, which runs the event, is a bit late to the party -- since three-quarters of small businesses are already active social media marketers, according to online marketing services firm Constant Contact, which surveyed 1,572 small businesses during March and April. Not only has social media become a major part of small businesses' marketing tools, Constant Contact reported, but the practice is increasing. Of the 73% of small businesses currently using social media, 80% said their use had increased during the past year -- and 81% said that it will increase over the next year. Of those that are not using social media yet, 62% said they plan to start during the next year. Facebook was the social medium of choice for 95% of the small businesses doing social media marketing, followed by 60% using Twitter, 58% using LinkedIn, 45% using YouTube and other video sharing and 23% using daily/local deal services. In terms of effectiveness, Facebook led again, with 82% of Facebook users finding it effective as a marketing tool -- followed by 73% for video-sharing users, 55% for daily/local deals, and 47% each for Twitter and LinkedIn. Contact said that small businesses seem to use social media as a complementary tool to other marketing efforts -- since it found that 95% of respondents use Web site marketing, 91% use email marketing, 77% use print advertising, 53% use event marketing and 69% use online advertising. The latter was the focus of American Express OPEN on Monday as it launched AdManager, an AdReady-powered platform designed specifically to help small businesses create, target and measure display advertising. The financial services company's small business division said AdManager would allow users "to optimize campaigns and maximize return-on-investment by shifting budget to higher performing ads." AdManager marks American Express OPEN's second online marketing app, following last year's debut of the Clickable-supported SearchManager campaigns for paid search.