"Our study shows that adolescents can be influenced by their friends' online pictures to smoke or drink alcohol," said Thomas W Valente, the study's principal investigator from the University of Southern California (USC). (Agencies)
"To our knowledge, this is the first study to apply social network analysis methods to examine how teenagers' activities on online social networking sites influence their smoking and alcohol use," said Valente.
Valente and his team surveyed 1,563 10th-grade students from the El Monte Union High School District in Los Angeles County in October 2010 and April 2011 about their online and offline friendship networks and the frequency of their social media use, smoking and alcohol consumption.
The researchers found that the size of one's online network of friends was not significantly associated with risky behaviour.
Exposure to friends' online pictures of partying or drinking, however, was significantly associated with both smoking and alcohol use, researchers said.
Teens whose close friends did not drink alcohol were more likely to be affected by increasing exposure to risky online pictures.
"The evidence suggests that friends' online behaviours are a viable source of peer influence," said Grace C Huang, study's first and corresponding author.
"This is important to know, given that 95 percent of 12 to 17 year olds in the US access the Internet every day, and 80 percent of those youth use online social networking sites to communicate," said Huang.
Students who responded to the survey were distributed across gender and on average 15 years old. About two-thirds were Hispanic/Latino and about one-fourth were Asian, which closely reflects the ethnic distribution of El Monte.
In April 2011, nearly 30 per cent of respondents had smoked and more than half had at least one drink of alcohol. Roughly one-third of students reported having at least one friend who smoked and/or consumed alcohol.
Almost half of all students reported visiting Facebook and Myspace regularly. Between October 2010 and April 2011, Facebook use (75 percent) increased while Myspace use (13 percent) decreased.
On average, 34 percent of students had at least one friend who talked about partying online and 20 percent reported that their friends posted party/drinking pictures online.
The study was published in the Journal of Adolescent Health.
"Our study shows that adolescents can be influenced by their friends' online pictures to smoke or drink alcohol," said Thomas W Valente, the study's principal investigator from the University of Southern California (USC).