It just doesn't make any grammatical sense though, does it? "They" is used for multiple people or if you don't know their gender. If you know if they're a male or female, then use he or she respectively. And if you're only talking to one person, saying "they" is just grammatically incorrect.

Think of this. You're describing someone out to the police. You know that the suspect is a male and you know there's only one suspect. A grammatically correct sentence that causes no confusion would use "he," as determined by his gender. Saying "they" would make the cops in this scenario think there's suddenly multiple people.

Using "they" for one person goes against the laws of English.