The language employed to describe sexual activity does reflect gender bias. A term like "player" (noted above) or "stud" or even "Casanova" or "Romeo" helps to bring a congratulatory notion to men who engage in such behavior. The idea of being a "ladies' man" is something to be praised and even in language does not sounds as bad. For women, this perception is worse. A woman who engages in such behavior gets labeled with terms like "whore" or "ho" or "dirty" as a way of describing how she is seen. The same moral and ethical purity regarding sex that we place on the shoulders of women are not shared by men. I think that this reflects a form of bias that has been a part of our culture for some time. The men receive an "Atta Boy" pat on the shoulder, while the women are subject to whispers, at best, that question moral structure and ethical behavior. Social modes of understanding through language such behavior does have gender bias attached to it.
Views of single men and women who are sexually active are usually very different. Single men who are sexually active are seen in a more positive way than females. When single females are sexually active they are seen in more of a negative way.
I agree that some common slang terms for men who are sexually active are player or stud. These names are not really negative. Males are often encouraged to participate in sexual activity and when they do so they are usually not seen in a negative way.
Some names for women who are sexually active are slut or whore. There are also very negative slang terms for older, single, sexually active women. All of these terms are very negative.
I would say that the words that we tend to use for sexually active males and females have very different connotations. These connotations show that we expect men to have sex and we expect women not to (outside of marriage).
The most common term for a woman who has sex outside of a committed relationship is "slut." That clearly has a negative meaning. It sounds really dirty.
Guys who have sex a lot get called a few things. Maybe the most common is "player." You can see how this sounds pretty positive. It sounds light hearted and fun.