Zynga Inc is buying OMGPOP, maker of the popular game Draw Something for an undisclosed sum, as the company moves to expand its games lineup on mobile devices and Facebook.

Zynga, which raised $1 billion in an initial public offering last December, makes some of the most popular games on tablets and smart phones such as Words with Friends.

New York-based OMGPOP makes the game Draw Something where players draw items or pop culture figures such as Lady Gaga or Katniss Everdeen from The Hunger Games books. It has 40 employees who will join Zynga as part of the deal, according to a statement.

In the six weeks since the game has been the market, it has garnered more than 35 million downloads and risen to the top of the app charts on Apple and Android, according to Zynga.

Zynga shares were up 60 cents, or 4.5 percent, at $14 per share on Wednesday.

(Reporting by Liana B. Baker; editing by Andre Grenon)