My pleasure!!!
Yes - many friends have reached out to me via the messages to even point out an error after it was published, which I'm open to! I don't find it as criticism. So I think it depends on who you are writing to.
One other note:
When you've written a draft -- click on the three dots...and there's an option for sharing a draft link - which you can email to a friend, or yes send a private message to the author you are trying to reach out to.
Note too: when you have subscribers - you have their email addresses. You can reach out to fellow writers via those emails - appropriately.
Lastly some friends send me private comments or fun talk via the private notes - and I welcome it! So know your author to understand how well they would welcome it.
For example, I followed a lady a long time ago but she has never read me or even interacted with me.
Recently a few days ago - she used this feature to alert me to a "raffle or give away game" on her website that I should go visit.
That I was bothered by:
1. She had never taken the time to ever read my articles.
2. She doesn't know me even on a basic acquaintance level
3. she wasn't giving me feedback
4. she used it to drive me to her website - and so maybe had she said something along the lines, "hey I hope I'm not bothering or if this is not of interest disregard" - but it felt spammy. She could have just sent it in a comment - but she probably knew it may violate some rule and didn't want to be reported.
But Medium lets us report those private messages too. So I did - to let her know, that that's just not the wise thing to do. She needs to read and write and reciprocate. Build relationships - then write an article and share her website - those who are loyal will follow her.
Sorry for the lengthy reply! Hope this helps! ;-)