Looking on the internet deeply has found these results:

Of mine who is the most popular phrase on the web.

Of mine whom 1149,000 results on the web	Of mine who 1682,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	A friend of mine who died today. I promised to take some food to a friend of mine who's sick. I also checked with a friend of mine who works organized crime back east. I just got done meeting with a friend of mine who knew Larry. I don't know if Niamh's mentioned it but I'm trying to raise a bit of money for a friend of mine who... And the friends of mine who make big, giant Hollywood movies say the reason their films are so successful is because of the brand partners that they have. By the way, a friend of mine who was here told me... ...about a place that's not too bad. I believe I mentioned a friend of mine who's suffering.

Of mine whom

1149,000 results on the web

Of mine who

1682,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

A friend of mine who died today.
I promised to take some food to a friend of mine who's sick.
I also checked with a friend of mine who works organized crime back east.
I just got done meeting with a friend of mine who knew Larry.
I don't know if Niamh's mentioned it but I'm trying to raise a bit of money for a friend of mine who...
And the friends of mine who make big, giant Hollywood movies say the reason their films are so successful is because of the brand partners that they have.
By the way, a friend of mine who was here told me... ...about a place that's not too bad.
I believe I mentioned a friend of mine who's suffering.