If someone is in Asia, it it appropriate to send ‘Hello Familyname?’ [on hold]

I need to communicate with users across the world, typically in the form of an email.

In Asia, many countries refer to someone primarily by their family name, with their given name coming second.

For example, the person that would be called 'John Chang' (if he was in an English speaking country) might be referred to as 'Chang John' in China.

Does this mean I should...

Use the first name - which is the family name, in an email greeting? Eg,

Hi Chang?

or use the last name, which is the given name, in an email greeting?

Hi John?