Small businesses are becoming more social. With social media, that is. Four in 10 business owners say they use social media platforms, including Twitter, Facebook and LinkedIn, as part of their marketing efforts, according to the American Express OPEN Small Business Monitor, a survey of 726 American small businesses from American Express OPEN.

That's a significant jump since last year, when only 1 out of 10 business owners said they openly engaged in social media, reported Aol Small Business.

The reason for the rapid embrace of the technology? Social media remain a free tool that allows businesses to offer two-way customer service, customer engagement and viral marketing - especially in a tough economy when traditional advertising and marketing budgets are often slashed.

"Now entrepreneurs are driving more business with existing customers through regular follow-up and better customer service," Susan Sobbott, president of American Express OPEN, said in a statement. This can be done via "relevant and low-cost marketing tools like social media."

And social media sites are even making a splash on business cards, suggesting that small businesses wants to spread the word about their social-media presence. In 2009, just 2.5 percent of cards featured a social media URL, according to Jason Keith, senior communications manager at Vistaprint. This year, it's up to nearly 4 percent, with Facebook being the most common. The upward trend of including social media sites on business cards suggests that businesses are actively capitalizing on such outlets as a way to drive traffic and boost sales.