First you have to follow them, then they need to follow you. Then you can message each other.
Sadly, both of you need to be following each other. Which is dumb in my opnion.
I assumed you were talking about somebody OTHER than a person you are following, so I went to Google and input this search string:
"blurtit user profile cookie roma"
It didn't take me to your profile page but it did find a number of comments you had made here. Had I gone to one of those comments and clicked on your name, it would have taken me to your profile page.
Clumsy, perhaps, but it'll work if you're looking for somebody. As long as you know their user name, of course.