Hi Von,
The word "netizen" is in fact used in English, primarily in British English. I've heard this word used by people from the UK, Australia, Singapore, and Hong Kong.
In American English, people often say that someone is an "online friend". I've heard this word used by people from the US and Canada.
While both "netizen" and "online friend" are acceptable, the expression "online friend" would probably be more widely understood.
Kind regards,
Greg