What are 'hey friends'?
My point being that 'hey' is quite separate to 'friends' and is an exclamation used to attract attention. Exclamations such as this are separated from other text by the use of a comma:
Jul 15, 2017 - 8:34AM
Nowadays, the trend is towards minimum punctuation in salutations.
In British English, many people omit the comma. I do!