• by David Goetzl  @dgoetzl, January 7, 2011

Interpublic Group CEO Michael Roth had to be saying "thank you Goldman Sachs" last week, while wishing again he had been more expansive when dealing with Facebook five years ago. Goldman's massive investment in Facebook gave Interpublic a windfall -- at least on paper -- but its coup could have been even greater with looser purse strings in 2006.

In mid-2006, when Facebook was still limited to college and high school students, Interpublic took a stake in the social-networking site that it pegged at less than .5%. Interpublic has never released any more details, including the amount it invested. But due to government filing rules, that suggests the amount is relatively low.

Roth said in 2008 that the investment had yielded "a nice profit," based on valuations in the market. Notably, the 1.6% stake taken by Microsoft for $240 million.

"Nice" is now a ludicrous understatement. Goldman dropping $450 million on Facebook last week helped push the site's value to $50 billion.

If Interpublic's stake is as low as .25%, its investment would be worth $125 million -- more than three times profit for the first half of 2010. The stake could be considerably less depending on the amount of shares Facebook has issued.

Still, Interpublic stands to do very well when Facebook goes public. At some point, when the investment becomes "material" to its results, it would report information.

"We wish (our stake) was a little bigger ... but at the time we invested in Facebook, we were doing it for strategic reasons to learn what was going on," Roth said in June 2008.

Interpublic's 2006 investment was part of a "strategic partnership" when Facebook said it had 8 million users, not the more than half a billion it has now. The deal gave Interpublic the opportunity to test advertising and marketing options on the site, as well as gather research and insight about young consumers moving away from traditional media.

At the time, Mike Murphy, then a Facebook vice president, stated: "We look forward to working with a partner whose values match so well with our own."

Values of a different kind were surely on Roth's mind last week.