Ten years ago this week, a 29-year-old entrepreneur named Jack Dorsey typed five words - "just setting up my twttr" - into a website and pressed Send. It was a fairly mundane debut for Twitter, which would go on to become one of the world's hottest internet companies. But Dorsey was hardly to know that. His previous start-ups had included a service to dispatch taxis and ambulances over the internet and a way to connect medical devices. So twttr (as it would be known until the company's founders shrugged off their disdain for vowels six months later) was by no means a guaranteed success.In the intervening years, the microblogging service has become an integral, some might say unavoidable, feature of millions of lives. It is the broadcast medium of choice for celebrities; it has built (and ruined) careers; and it is where news breaks before anywhere else: a recent study suggests emergency services can track storms and earthquakes faster using Twitter than traditional monitoring tools.The service is closely associated with major events and cultural movements, including the 2011 London riots, the Arab Spring, the Black Lives Matter movement and Barack Obama's 2008 grassroots ascendance to the White House. And for nine of Twitter's 10 years it was the darling of the technology world .But the past 12 months have not been kind to Twitter. At the time of its IPO on the New York Stock Exchange in 2013, analysts feverishly predicted that Twitter could ride the same trends that had made Facebook a $100-billion internet powerhouse. But the reality has been starkly different. Two-and-a-half years later, Twitter's user base is a fifth the size of Facebook's and has essentially stopped growing.Despite the service's apparent simplicity - write a message of up to 140 characters and publish it, and follow people to see their tweets - a hidden complexity means that new users often find Twitter baffling. The service's unwritten rules of engagement, the work that new users have to put into following the right people, and the frantic nature of Twitter's real-time feed of messages, can be confusing to the uninitiated.In the past 12 months, Twitter's share price has crashed. Last year, the company returned to the past by replacing its chief executive of five years, Dick Costolo, with Twitter's visionary founder, six years after Dorsey had himself been removed.The new leader has cut jobs, presided over a management exodus and reconsidered the fundamental and much-loved features that have served Twitter for the past decade. Last month the service began showing users tweets arranged by an algorithm, rather than the simple chronological feed of messages people are used to.But Dorsey has so far failed to bring about the Steve Jobs-esque revival in Twitter's fortunes that was hoped for, at least when it comes to the number of people using the service.However, Dara Nasr, Twitter UK's managing director, says Dorsey has had a hugely positive effect on the company."I'm more excited about Twitter than I ever was before and a lot of that is due to Jack and his vision," Nasr says. "What he's done is recognised there need to be changes."He's been very clear to investors that things need to change - they'll take time but there's a plan in place and that's resonated."However, growth has been flat for the past six months, standing at around 320million users.Nasr says Twitter still has a not-unimpressive reach, especially when you count the 800million people or so the company claims are "logged-out users" - those who do not have accounts but might use the service anyway, or see tweets elsewhere on the internet."It's not a small figure, it's very much a global product, but yes of course we'd like to grow."What we want to do is show the respect and love we have for our existing 320million users and also open the door for other users," says Nasr.He points out that Twitter is busier than ever: when Leonardo DiCaprio finally won an Oscar last month, there were 440000 tweets a minute, a record for the service. Twitter representatives point to its power as an incubator for campaigns that have incited change and fostered solidarity, such as #JeSuisCharlie, in response to the Charlie Hebdo attacks in Paris last January.Last week Kim Kardashian, one of the world's biggest internet celebrities, said Twitter was the place "where I can freely talk and have conversations with anyone and everyone".But some users feel that Twitter has become a hotbed for online abuse, with harassment and bullying affecting their enjoyment of the platform.Nasr says the vast majority of tweets are not problematic, but: "If you were to hold a mirror up to society, society's not necessarily lovely." He said Twitter will be doing more to combat trolling.Dorsey has outlined several other priorities for Twitter, including the growth of Periscope, an app that allows smartphone owners to broadcast live video.Although the decline in Twitter's share price has levelled off in recent weeks, the man whose five-word message began a huge social phenomenon has made it clear that massive changes are in the offing.When most companies enter their second decade, their most volatile days tend to be behind them. But for Twitter the biggest tests could still lie ahead.- ©The Daily Telegraph..