The Collaborative International Dictionary of English v.0.48:

Sensationalist \Sen*sa"tion*al*ist\, n.
   1. (Metaph.) An advocate of, or believer in, philosophical
      sensationalism.
      [1913 Webster]

   2. One who practices sensational writing or speaking.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sensationalist
    n 1: someone who uses exaggerated or lurid material in order to
         gain public attention [syn: sensationalist, ballyhoo
         artist]