The numbers were revealed during a call with journalists by Twitter CEO Dick Costolo, who claimed that the firm will remain independent and increase its revenues through advertising.
"We want to be able to remain independent, grow the business the way we want to, and not be beholden to public markets until we feel like we want to be," he said, according to Reuters.
Costolo also revealed that Twitter's plans to increase advertising on the service were going well and are likely to continue to do so. "We now feel that based on the engagement rates we're seeing ... that we're ready to expand this further," he added, suggesting that users could be exposed to ads from companies that they do not follow.
"It's our firm belief that our advertising platform is the only revenue component that we need to have in the market in order to be a huge independent business."
The 100 million users, a number that is dwarfed by Facebook's userbase, are each posting at least once a month, according to the firm, but overall Twitter has around 200 million registered accounts. Half of the active users log on at least once a day, Costolo added