Smurfette is the only male smurf.
Speaking as a population, details like long hair and hips and a high voice are not necessarily gender indicators. Let us not forget the peacock, after all, or many other birds, where the ‘pretty’ bird is the male (so he can better attract mates, and, after having done that, distract predators from his progeny). To look at the smurfs as a population, Smurfette is a member of one gender (we assume), and the others are members of another.
Smurfette’s gender is indicated by pronoun usage – the smurfs do indicate her as different for some reason. However, as a population, any long-term community with newcomers is not going to survive with only one breeding-feasible creature. There’s nothing to indicate that smurf gestation period and mating habits are wildly out of whack with what we’re used to. If a smurf were to be born ‘fully grown’ very quickly, it would ask for a lot of resources and take a lot of toll on its ‘mother.’ They’re complex organisms, things that work for ants won’t work for them.
So, assuming that Smurfette is a different gender, and assuming as complex organisms the smurfs have a reasonable gestation periods, the conclusion that makes the most sense to me is that Smurfette is, in fact, male – and every other smurf is female, responsible for the gestation and development of young. This explains how the population can grow and why the smurfs themselves have such homogenity – there are always new smurfs being born, off-screen, because Smurfette’s always spreading his gamtes.