In fact only a few were really shot down by Stingers. Soviets were pretty quick with effective countermeasures.
Here’s a link to an article listing 74 Hi-24’s lost in Afghanistan, along with 14 ‘unidentified’, some of which must have been Hi-24’s.
It does not say whether they were lost to Stingers, or any particular weapon.
http://en.wikipedia.org/wiki/List_of_Soviet_aircraft_losses_in_Afghanistan