In a large social media corpus (2.9 million tokens), we analyze Flemish adolescents’ non-standard writing practices and look for correlations with the teenagers’ social class. Three different aspects of adolescents’ social background are included: educational track, parental profession, and home language. Since the data reveal that these parameters are highly correlated, we combine them into one social class label. The different linguistic practices emerging from the analyses demonstrate the crucial impact of social class on adolescent online writing practices. Furthermore, our results nuance classical findings on working class adherence to ‘old vernacular’ by also highlighting working class youth’s strong connection to the online writing culture, or ‘new vernacular’. Finally, we point out the complexity of the social class variable by demonstrating interactions with gender and age, and by examining groups of teenagers whose social background is ambiguous and therefore hard to operationalize.