Online messages often diverge from the standard language orthography: so-called textisms have become an indispensable part of youths’ written computer-mediated communication (CMC). This paper presents an in-depth corpus study of texts from four new media produced by Dutch youths: MSN chats, text messages, tweets, and WhatsApp messages. It is demonstrated that Dutch informal written CMC, as in other languages, is implicitly governed by orthographic principles. Relative frequencies of textism types in the corpus show how textisms are effectively used by Dutch youths. Textism types are classified here in terms of forms, operations, and, crucially, functions – the ‘SUPER-functions’: textisms can make orthography more Speechlike, Understandable, Playful, Expressive, or Reduced. Moreover, this study proves that preferences for textism types greatly depend on age group and medium. New media have their own combination of characteristics and constraints, while adolescents and young adults appear to have different perceptions on language use and spelling.