Nearly one in four teenagers are ‘almost constantly’ online as their lives are swallowed up ever more by their mobile phones, a study has revealed. Some 24 per cent of 13 to 17-year-olds admitted they were continuously checking their devices, including when they were at school. Nine in teenagers also confessed to going online every day as they were unable to resist the lure of Facebook and Instagram. In danger? The study also looked at social media and found that middle class teenagers were more likely to use Snapchat, the controversial message service where messages disappears seconds after they are sent . Parents now find it increasingly difficult to monitor their children's online behaviour as more than 70 per cent of teens use now more than one social network. The study was carried out on American teenagers but the findings would likely be worse in the UK as more British teenagers own smartphones than their US counterparts. The Pew Research Centre asked 1,060 children aged between 13 and 17 about their phone habits. The report found that what Pew described as a  ‘frenzy of access’ was facilitated by mobile phones - particularly smartphones. Of the 92 per cent of teens who went online every day, more than half said that meant using their phones several times a day. Some 12 per cent admitted to using a gadget once a day, six per cent said they went online just once a week and a mere two per cent said it was less than that. Addicted: Overall Facebook remains the most used social media site among teens with 71 per cent using it . In the largest ever systematic study of emails - examining more than 16 billion messages - researchers have found that most people send replies containing just five words. The study, which was conducted by researchers at Yahoo Labs and the University of Southern California, also found that our email habits also follow remarkable patterns. Replies become faster as the conversation progresses, but the researchers found they could tell when a email thread was about to end as the last reply was much slower than the previous replies. 'The long delay in a reply could be considered as a signal for the end of the conversation,' said the researchers, led by Farshad Kooti, a computer scientist at the University of Southern California. The study examined the emails sent by two million Yahoo users over a period of several months. They found that on average younger people tend to spend less time composing an email - with a reply time of around 13 minutes on average for teenagers. Young adults take 16 minutes, while those aged 36 to 50 years old spend around 24 minutes before sending their reply. Phone ownership was almost ubiquitous among young people, meaning they grow up used to being able to access anything any time they want. The Pew study found that nearly three-quarters of teens have access to a smartphone. Some 30 per cent have a basic phone and just 12 per cent of 13 to 17-year-olds have no phone of any kind. The study also looked at social media and found that middle class teenagers were more likely to use Snapchat, the controversial message service where the text and images disappears seconds after they are sent. The service has been blamed for a rise in ‘sexting’, where young people send explicit pictures to each other. Overall Facebook remains the most used social media site among teens with 71 per cent using it. Amanda Lenhart, the lead author and associate director of research at the Pew Research Centre, said: ‘There’s been a huge diversification of social media. ‘If you are wondering where your child is, you probably need to cast a wide net, because there is a variety of places where your teen could be spending his or her social media time’ Previous studies have starkly illustrated the extent to which young people are addicted to their mobiles. Smartphone users check their devices an average of 150 times a day as they cannot bear to be apart from them, one research paper showed. The study showed that we are so addicted to their mobiles that we cannot go 10 minutes without fiddling around with them.
9 in 10 teens go online every day, unable to resist the lure of Facebook .
Parents also face a nightmare monitoring children as 71% of teens use more than one social network, the Pew Research Centre found .
Nearly three-quarters of teens have or have access to a smartphone .