It works ok for me, providing as you put something in the Search For: window e as Eddy said, will be in every post. Then the only problem is getting the By User: (username) correct.
A case in point being Eddy, because that is his Screen Name and not his Username.
To find a correct username, you need to click on the screen name which will display the user profile, which will show the username for a search.
One advantage of opening the user profile is you can display the last n (n being a variable number you can select) posts by the person. So you may not need to do a search.