The Collaborative International Dictionary of English v.0.48:

Seducer \Se*du"cer\, n.
   One who, or that which, seduces. For a female seducer, the
   term seductress is also used
   [1913 Webster +PJC]

         He whose firm faith no reason could remove,
         Will melt before that soft seducer, love. --Dryden.
   [1913 Webster]

   2. Specifically: One who induces another to engage in sexual
      intercourse.
      [PJC]

WordNet (r) 3.0 (2006):

seducer
    n 1: a bad person who entices others into error or wrongdoing
    2: a man who takes advantage of women [syn: seducer, ladies'
       man, lady killer]