When you are writing about a celebrity or other person you do not know personally, please use their last name when referring to them in your article.
I have seen an increasingly prevalent trend in submissions for authors to use the first names of people they do not know, especially women. Just as Donald Trump would be referred to as "Mr. Trump," or simply "Trump," in a biography about him in Forbes magazine, so should Hillary Clinton be referred to as "Clinton" or "Mrs. Clinton." Surnames, especially when preceded by a title, are used as a sign of formal respect. Using the first name of a person by an author who does not know a person to a general audience who does not know a person does not extend the formal respect expected from professional writing.
While gossip magazines may refer to the household-name celebrities like Paris Hilton by their first names, these personas have become to be known by these names because their names, and their characters, are so unique they could not be confused with anyone else. However, it would be rare for a magazine like Vogue to refer to Tom Cruise as "Tom." "Tom" is a common name. In addition, as strange as he is, he is not commonly referred to by his first name, nor does his notoriety make everyone who hears the name "Tom" think of Tom Cruise.
Of course, when individuals have chosen to use their first names or single names as a way of defining themselves (Cher, Madonna), they may be referred to in this way. People who hear the name "Cher" will automatically think of the performer, unless they have a close friend or relative who goes by the same name.