Social media are viewed as having potential for agricultural extension. This study therefore surveyed social media use by farmers in a developing country, and their role as a source of agricultural information. To this end, 365 farmers in Chiang Mai, Thailand, were sampled and interviewed using a questionnaire. The findings revealed that the majority of respondents (81.92%) did not adopt social media and, these remained marginal as a source of agricultural information for farmers. Those using social media (18.08%) employed certain applications, i.e., LINE, Facebook and YouTube, mainly for communication, new updates and entertainment. Younger farmers and farmers with a higher formal education related to social media use significantly. To fully harness the potentials of social media for agricultural extension, more farmers need to be encouraged to use them, while relevant agencies also are required to provide support for this effort, such as staff training in social media use, and enabling a social media policy.