personal pronouns - What do you say when you don't know someone's gender?

For example, I want to refer to someone on the internet, but I don't know this person's gender. Which personal-pronoun do I use? (as article I mean he, she, it, etc)

Answer

It's perfectly fine to use they in the singular sense. (Verbs are conjugated the same as they would be in the plural sense: "are they joking?", "did they break anything?".)

All the same, when the gender is not known, some authors prefer constructions like (s)he, he/she, he or she, she or he, etc., some prefer to stick with the masculine pronoun as default (he), others prefer to stick with the feminine pronoun for balance (she), some will alternate using he and she in their writing.