Postal and telephone survey research is threatened by declining response rates and high cost. Online recruitment is becoming more popular, although there is little empirical evidence about its cost-effectiveness or the representativeness of online samples. There is also limited research on optimal strategies for developing advertising content for online recruitment. The present study aimed to assess these aspects of online recruitment. Two mental health surveys used advertisements within a social network website (Facebook) to recruit adult Australian participants. The initial survey used advertisements linking directly to an external survey website, and recruited 1283 participants at $9.82 per completed survey. A subsequent survey used advertisements linking to a Facebook page that featured links to the external survey, recruiting 610 participants at $1.51 per completion. Both surveys were more cost-effective than similar postal surveys conducted previously, which averaged $19.10 per completion. Online and postal surveys both had somewhat unrepresentative samples. However, online surveys tended to be more successful in recruiting hard-to-reach populations. Advertising using “problem” terminology was more effective than “positive” terminology, while there was no significant effect of altruistic versus self-gain terminology. Online recruitment is efficient, flexible and cost-effective, suggesting that online recruitment has considerable potential for specific research designs. Copyright © 2014 John Wiley & Sons, Ltd.