Teens who access the internet through their phones are also more than twice as likely to engage in sex with a person they met online than those without access.
Those with smartphones are also more likely to be sexually active in general, and more likely to say they had been approached for sex online, the Daily Mail reported Wednesday.
Researcher Eric Rice, from the University of Southern California's School of Social Work, said that while smartphones do not directly cause teenagers to engage in potentially risky sexual behaviour, they do make it easy.
Rice said that, while parents have come up with strategies to monitor the online behaviour of their children on computers, they also needed to take account of the internet access provided by a smartphone.
The study involved about 1,840 high-school students in the Los Angeles unified school district who were surveyed in the 2010 to 2011 school year.