It’s been revealed that the number of people who use Twitter has grown to 100 million.

Twitter CEO, Dick Costolo, announced the news during an interview at the Web 2.0 Summit held in San Francisco on Monday evening.

It’s been nothing but growth for Twitter over the last year or so. In June the company announced that it had surpassed the 200 million tweets per day milestone, double the number it was seeing in January 2011. Since then it has leapt to almost 250 million tweets per day.

This surge in activity can be associated to the fact that of Twitter’s 100 million active users, over 50 percent currently login daily. At the start of the year, users logging in daily stood nearer 30 percent.

During his speech, Costolo also revealed that Twitter signups via iOS devices (iPads, iPhones & iPods) have tripled since the launch of Apple’s new mobile operating system – iOS 5.

The new operating system, that launched earlier this month, integrates deeply with the social network to allow users to, amongst other things, sync their Twitter friends with their phone book, tweet friends from within the contacts app and tweet out web pages directly from Safari. To help matters still, iOS 5 even prompts users to download the official Twitter app in the settings menu.

Prior to launch there were suggestions that Apple was working with Twitter but to what extent was unknown, now it’s become clear and the integration seems to have paid off.

In response to the successful relationship, Costolo said, “We all anticipated it’d be big, but the integration is so native and feels so frictionless. It was even better than we thought.”

It’s been a successful year for Twitter so far and if the company’s ambitions are anything to go by, expect more of the same going forward. Costolo said, “We have lofty ambitions. We want to be part of the fabric over every communication in the world, and we think we can reach every person on the planet.”