A Playboy is what we´d said a "Casanova" or "DonJuan", I think these are the most common meanings for that word.

You cam possibly say "mujeriego", "conquistador", "vividor", "donjuán" or "seductor". There's many ways to say it and it also usually depends on what sort of Spanish you are talking about since they probably have different names for in Spain than they do in countries like Mexico.