A yoyo is currently a useless item, and often considered as junk.
Pink with a yellow star in the center, a yoyo has no use and has been added purely for the purpose of clutter, creating more realism for the player when looting.
A yoyo can be found in bedroom cupboards, desks, school lockers, gloveboxes of vehicles and very rarely as loot on zombie corpses.
From newitems.txt (Project Zomboid directory/media/scripts/)
Weight = 0.1,
Type = Normal,
DisplayName = Yoyo,
Icon = Yoyo,