Judith, if I want to find posts a specific person has made I look at their user profile page.
I spun off a new topic called 
How to find posts & other activity for a particular person. The post tries to explain the steps I use to view a person’s user profile page.
Of course, this may be something you (and @Holger) already knew, But I figured it still might be of use to help some other folks find their way around. 