What's the feminine version of womanizer?
Man-eater and vamp are a little bit "slangy" compared to
Per Neil's comment to the question itself, bitch isn't really relevant to the meanings involved here.
Per comments/discussion below, it's probably impossible to come up with a "feminine version of womanizer" that only switches the gender without implying other differences. Language reflects social attitudes, biology, etc., so even a structurally trivial distinction such as seducer/seductress unavoidably entails gender-based preconceptions that OP is probably seeking to avoid.
Man-eater is one term sometimes used.
[INFORMAL] a dominant woman who has many sexual partners
One that comes to mind is man-chaser. Another common slang term with a similar meaning is boy-crazy, though it doesn't have the same sexual connotation.
A natural follow-up question is, "why is there no such word as manizer?" There is a language log post that discusses the coinage of this word, with the main argument against manizer being the awkwardness of the monosyllabic root with the -ize suffix. The comments suggest a number of interesting alternatives.
Wanton is probably the closest term. Dictionary.com define the word as "a lascivious person, especially a woman." There's a good discussion on "What is the female equivalent of 'philanderer'? on Quora, and it explores the complex nuances involved in comparing the sexes in this regard.
Personally, I like female Don Juan, a term applied to Carla Bruni in a recent biography. The term coveys a sense of direct power and control that is typically is missing in describing women who have multiple sexual partners.
I suggest "loose woman" as an alternative to the very derogatory term "slut." Although "loose woman" also carries a sermonizing attitude, neither is such an implication entirely absent from "womanizer." The latter is certainly not a term of praise.
Were it not for the usual sexual asymmetry present in our language and culture, "loose man" would be a reasonable synonym for "womanizer."
I also agree with the suggestion above that "man-chaser" is a good equivalent, and probably better than "loose woman."
Please excuse me if you find these terms profane but, my grandmother would refer to woman who chases men as a slut, although this is sometimes used to describe a girl as dirty or messy. I do recall a man using the term to describe another who was especially open and active in his choice of bedfellows.
I've often heard the rather coarse term slag used as slang but I would suggest this reflects negatively on the user.
I assume these both share a common route with the old fashioned term slattern which in turn leads me to consider harlot, brazen hussy or trollop.
Slut. Slut: Disparaging and Offensive. a sexually promiscuous woman, or a woman who behaves or dresses in an overtly sexual way.
Not the nicest or most proper word, but IMO definitely the most accurate.
might not be a bad choice either. Although it tends to be gender neutral, it seems to be used more commonly with reference to women.
promiscuous: Characterized by or involving indiscriminate mingling or association, especially having sexual relations with a number of partners on a casual basis.