Although many studies have been carried out on advertising effectiveness, there has been little research as yet on the effectiveness of social advertising, and even less in the context of social networks. In this article we aim to discover which models of persuasive communication are most effective in making social media responsive to a young audience. Our starting-point for this purpose was a study of 370 advertising messages from the leading Spanish NGOs. By tabulating these messages statistically we were able to define two models of persuasive communication in networks: a connotative model and a denotative model. These were subsequently validated by a focus group comprising communication managers from various NGOs. Our object was to find out which of these models proved most effective in terms of involvement and virality. To do so, we designed an online experiment based on simulation. First we created a fictitious Facebook page for the NGO Movimiento por la Paz (�Movement for Peace�), having obtained its prior consent. Then we invited a group of young people, heavy users of social networks, to visit this page and interact with it. Finally, we analysed all the activity carried out by the subjects in the sample, using two tools: quantitative analysis of interactions (number of visits, impressions, comments, use of the �Like� button, content published on the Wall, etc.), with the aid of the metrics provided by Facebook Insights, and through analysis of the content of comments posted by users. The results clearly favoured the connotative model