Zapala is a town in Neuquen province that can probably be classified as the south of Argentina, which implies that hitchhiking there sucks.
At 23:00 there is a collectivo to Neuquen, and it stops if you wave clearly enough. However, Neuquen is not a much better place for hitchhiking.
RN40 South toward Junin de los Andes/San Martin de los Andes
There's a round-about in front of the Casino Black Gold where pretty much only local traffic passes. From there, you can walk along the road out of town for about 800m just past the turn to the railroad tracks where some cars slow down a little bit. Cars pass quickly, but there's plenty of room for them to stop, very little traffic, and they'll see you from far away. A sign showing desperation (i.e. "donde sea") might help.