Some of the Smurfs get turned into gold coins by Gargamel which get stolen by thieves.
Did You Know?
In "Smurfette Unmade," Gargamel thought of turning Smurfette back to her original self was something he never though of previously. However, in "Smurf Colored Glasses" (from Season 1), he almost did change Smurfette to her original self until an unexpected visit by a hungry Bigmouth stopped him. See more
Smurfette, stop sniffling.
But poor Sassette... Oh I have been so selfish... I'll never forgive myself...!