What you want is "people are concerned about what famous people do" "To be concerned about" means that the subject of the sentence, here "people" have a concern. "To concern" means to cause concern, not to have it. A better word than "concern" here is "interest" and it's used in the same way: "to be interested in" and "to interest". Using interest, you could write your sentence two ways. Notice that the subject and object are reversed. "What famous people do interests people." "People are interested in what famous people do." Or some sentences where "concern" is the right verb choice: "What my kids do concerns me." "I am concerned about what my kids do."