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]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "seducer":
   Artful Dodger, Casanova, Circe, Don Juan, Lorelei, Lothario,
   Machiavel, Machiavelli, Machiavellian, Parthenope, Romeo, Siren,
   actor, amoroso, bamboozler, beau, befuddler, beguiler, betrayer,
   boyfriend, caballero, cavalier, cavaliere servente, charmer,
   coquette, counterfeiter, debauchee, debaucher, deceiver, defiler,
   deluder, despoiler, dissembler, dissimulator, dodger,
   double-dealer, duper, enchanter, enchantress, enticer, entrancer,
   esquire, faker, fellow, femme fatale, flame, flirt, fooler, forger,
   gallant, gay deceiver, gigolo, heartbreaker, hoaxer, hypnotizer,
   inamorato, inveigler, jilt, jilter, joker, jokester, kidder,
   lady-killer, lecher, leg-puller, libertine, love-maker, lover, man,
   masher, mesmerizer, misleader, necker, old man, petter, philander,
   philanderer, plagiarist, plagiarizer, playactor, playboy,
   practical joker, ragger, raper, rapist, ravager, ravisher,
   role-player, roue, seductress, sheik, siren, skirt chaser, spoofer,
   squire, sugar daddy, swain, tease, teaser, tempter, temptress,
   vamp, vampire, violator, wolf, woman chaser, young man