Deals for Gamedoctors, Page44 Studios, HipLogic and Astro Ape Studios concluded with minimum fuss.
Reuters has been trawling through the filings and discovered that the Facebook gaming giant has been hoovering up a bunch of mobile firms.
Zynga's mobile chief David Ko then confirmed the acquisitions.
Specifically they include: Germany's Gamedoctors, best known for ZombieSmash; SanFran's Page44 Studios, which is behind the World of Goo game, HipLogic, the US UI specialist behind the Spark interfact; and New York based Astro Ape Studios.
Zynga has expanded at a dizzying pace to become one of the biggest gaming companies in the world. But the sheen has come off a bit in recent months, with subscribers dropping away and new games failing to match expectations.
In November, it was reported that Zynga had 54 million daily active users overall in Q3, down from 59 million in Q2.
The share price has fallen correspondingly.
Zynga was expected to pursue mobile more energetically than in has, especially in the light of the pace set by EA, Gameloft, DeNa and others.
It did a very public deal for UK-based Wonderland last year, but these deals confirm its desire to play more directly in the mobile space.