The company, founded two years ago, has exploded in popularity but has held back from introducing ways to monetise its internet traffic. Its founders have said they wanted to concentrate on growth and not alienate account holders.
Users of the service post short messages, limited to 140 characters, and can choose to follow the streams of updates from other users. The service has attracted increasing interest from businesses and marketing companies, keen to make use of its "real time" news value.
Co-founder and chief executive Biz Stone said there were no immediate plans to introduce advertising but the company wanted to "keep our options open".