Younger adults in Australia are gaining more weight and increasing waist circumference faster than other adults. Despite this, engaging 18-35 year olds in interventions aimed at prevention of weight gain is challenged by limited reporting of successful recruitment strategies. This paper describes the effectiveness and cost of recruitment strategies employed in a multi-site randomised controlled trial (RCT) testing the efficacy of a mobile-phone based program ‘TXT2BFiT’ designed to prevent weight gain among young adults. The planned protocol was to invite three Medicare Locals in the Greater Sydney Area to recruit 24 General Practitioners (GPs), with each to contribute 15 participants. However, the response was slower than previously experienced when recruiting GPs for RCTs with middle-aged adults and additional strategies were introduced. These consisted of electronic newsletters at universities; posters at universities, TAFEs and community locations; newspaper advertisements and electronic media (social and advertising) of Facebook and Google. In total, from 1181 enquiries, 250 participants were randomised. A total of 5311 letters of invitation were sent from 12 practices (16 participating GPs). One hundred thirty one patients enquired with 68 participants randomised (52% enrolment). The other recruitment methods yielded the remaining 182 randomised participants. The enrolment from print media was 26% of enquiries, from electronic 20% and from other 3%. The total cost of recruitment was $126 (AUD) per person. The least expensive modality was electronic, largely due to a free feature story on one university web homepage, whereas Facebook cost $896 per enrolment. The most expensive was print media at $98 and GPs cost $88 per enrolment. The possible disadvantage of low recruitment from GPs is that those of lower socio-economic status become underrepresented so future research will include how to better engage GPs in lifestyle interventions for young adults. News media appear to have wide reach at no cost.