The presence of cyberspace in the lives of young people is such that we can no longer distinguish between online and offline spheres. They live a process of onlife development that is not always equitable in terms of gender. This paper aims to account for the online behaviour of Spanish adolescents according to gender and age, the decisions they make when constructing their virtual identity, and the effects that this has on them. A quantitative study has been carried out at a national level (N=2,076, 12-18 years old) following a non-experimental ex post facto design by means of a survey study. The results show that there are gender differences in the preference for one or other social network. A high percentage of girls make different choices when it comes to their online presence. Unlike boys, girls state that their virtual self and their behaviour significantly influence the opinion that they have of themselves and their need to feel integrated. In conclusion, the decisions that adolescents make when creating their virtual selves do not only have negative consequences derived from poor management, but are also plagued by mandates and stereotypes that determine how they should be and what they should do online; something that is especially pressing for girls.