Others use the plural, i.e. "they" even when you're talking about a singular person. I use this approach myself. It's very common, but there are people who oppose it.
Now the word 'yo' is used as a general hello, e.g. when Baby Bush had the famous "Yo, Blair" incident. However it's been reported in the news that some children are starting to spontatneously use 'yo' in place or 'he' or 'she'.
Here's a New Scientist reference, for example.
The article points out that one feminist opposes this word, thinking that it is disrespectful.
It seems amazing to me that no matter what approach people take in language, there are some who oppose it. I would have expected a feminist to be delighted that a new gender-neutral singular pronoun had spontaneously arisen.
I am happy to use 'yo', or any other word that's generally accepted. In the meantime I'll continue to use 'they/their'.