The average English speaker probably doesn’t realise that ‘xoxo’ means nothing to people who don’t speak English. Even my French friends who spoke English really well, and understood that an ‘x’ was a kiss and an ‘o’ was a hug, didn’t really understand how those two letters represented a kiss and a hug.
In France, the ‘xoxo’ equivalent is ‘bisous!’ (meaning kisses!) and can be used with everyone. You can shorten it and write ‘biz’ to make it more casual. If you want to step it up a notch you can write ‘gros bisous’ (literally fat kisses) or if you want to be a little romantic, you can write ‘je t’embrasse’ (I kiss you).
I don’t really remember how it came up, but whilst I was dating Matthieu I had to explain how to write ‘xoxo’ when we sent text messages.