Twitter advertisements, which, anecdotally, have proven to be highly effective in boosting sales, will be available to more small businesses come March.

The company is partnering with American Express to set up a long-awaited self-service advertising program. Initially, the program will only be available to merchants who use and accept American Express cards, and American Express is offering $100 in free advertising to the first 10,000 companies to sign up for the program.

The advertising program is set up to mimic Google's successful AdSense platform, as well as a similar program on Facebook. But that's where the Facebook mimicry ends: in an interview with the Associated Press Thursday, Twitter CEO Dick Costolo reiterated previous comments about the company's plans to file an initial public offering.

"I don't look at what other companies are doing," he said. "We don't think in terms of building this company for a particular IPO date. We are trying to build this company for the long term."

Previously, advertisers had to go through a sales representative to purchase ads, which are called "promoted tweets" on the site. Despite the extra steps, advertisers have flocked to the program.

Glennz Tees, an online merchant in Austin, Texas, told the Associated Press that December sales doubled after they started advertising on Twitter. The company posted just three ads a week and, in addition to the sales boost, saw the number of followers of its Twitter account triple.

Research firm EMarketer expects Twitter to generate revenue of $260 million this year, nearly twice the $140 million it generated last year.