IPG has been quiet about its stake in Facebook. As marketers are still looking for the best ways to approach the social network’s the ad holding company’s connection is certainly helpful. It’s also noteworthy given how early in Facebook’s existence the investment was made. The social net, which was founded in 2004, now has about 600 million users.

Still, IPG’s 0.4 percent stake in Facebook is dwarfed by others — but not by much. For example, Microsoft (NSDQ: MSFT) has an estimated 1.3 piece of Facebook for a $240 million investment, while Russia’s DST bought in at a $10 billion valuation, has a 10 percent stake in the social net.

Unlike rival ad holding companies Publicis Groupe and WPP Group, IPG has been relatively limited in its interactive investments and acquisitions. Given formation and subsequent restructuring of its Mediabrands unit, which functions as an umbrella over its media buying and digital agencies, over the past two years, that could change as it has put its digital leadership team in place.

In January, after a year of looking for a CEO at Mediabrands, the company looked in-house and selected Universal-McCann’s Matt Seiler as the unit’s head. Leading up to that decision, digital vets Sean Finnegan was tapped to lead hyperlocal subsidiary Geomentum and Tim Hanlon was picked to manage Velociter, the venture capital arm. Velociter is expected to raise IPG’s investment profile over the course of this year, especially as the M&A digital market continues to heat up.

Yesterday, Mediabrands, which serves as the digital and media hub for all the IPG media agencies, moved UM’s Matt Seiler over to fill the year-long vacant CEO post. The changes don’t have much to do with each other, though it does serve to highlight the ad holding company’s deeper digital push compared to a few years ago, when WPP and Publicis Groupe seemed to be pointing the way in terms of digital integration.

As for Hayes’ new role, he will help shape the design and evolution of the agency’s worldwide performance model. On that front, he’ll work with Eric Bader, who was hired by Initiative a year ago to serve as chief strategy officer. Hayes will be based in Los Angeles and report to Tim Spengler, president, Initiative North America, and Bader.

Rally will be charged with conceiving ad campaigns around social media, as well as measuring buzz and effectiveness about clients’ brands, the WSJ reported. The new unit will be headed by Heidi Browning, who left MySpace (NSDQ: NWS) as SVP for insights and planning last October to take on the role of global digital officer for IPG’s Universal McCann.

Publicis Groupe is also in the process of starting a dedicated social media unit within its digital hub, VivaKi. The new social media unit will pull in executives from around the agency to spur more collaboration. It should be up and running by the end of the year.

But as the ad agencies build up their social media bona fides, they’re also seeing increased competition from an unfamiliar quarter. Meredith (NYSE: MDP), which last week bought up the remaining shares of mobile marketer The Hyperfactory, has seen its New Media Strategies subsidiary attract a lot of business lately from blue chip clients like Chrysler and Domino’s Pizza.

PR agencies are also challenging agencies for social media business to some extent. But ad agencies and PR firms are likely to be hampered somewhat in their attempt to include social media marketing as a distinct business. Rather than coming up with clever taglines and eye-catching creative, or in simply reaching out to blogs with news about a client, social media marketing is largely about customer relationship management. In the case of Domino’s, it decided to go with NMS, the Meredith unit, because it specialized in word-of-mouth marketing.

Still, the big agencies do possess one considerable advantage: their continued deep pockets, which allow them to target startups who appear to have figured out the social media space for acquisitions. M&A activity around marketing services led to a boost in deals over the first half, and while the economy remains shaky, the third and fourth quarters are likely to experience a particular uptick in transactions by agencies around social media.

IPG CEO Michael Roth said as much during the company’s Q4 earnings call late last month. He particularly cited Latin America, China and India as locations that IPG would look to acquire digital agencies. Historically, IPG has spent $150 million or less on acquisitions and he indicated that he would use that figure as a guidepost for what the company would be spending on future purchases.

IPG probably didn’t spend that much on Cubocc. The Brazilian shop has about 150 staffers. IPG considers it a natural fit, since the six-year-old Cubocc handles major marketers like Unilever, which splits its business across IPG, WPP and Omnicom. While Cubocc will continue to service and compete for its own business, IPG will look for ways the two can partner. The firm will continue to be led by its founding partner, Roberto Martini.

IPG hasn’t done a lot of digital M&A activity over the past few years. In July ’08, it did acquire a stake in digital design and marketing firm Huge, which is based in Brooklyn, NY. More recently, IPG has been trying to put a formal team in place to chart digital ad growth and investments.

Digital ad vet Matt Freeman was hired earlier this year to oversee IPG’s interactive media unit, Mediabrands Ventures, which the ad holding company established to spur innovative ideas and collaboration among its various agencies. One of the responsibilities Freeman is charged with is finding independent digital companies that might be a good fit for IPG. Release

Before heading to Brand In Hand in January 2007, Bader was the top digital executive Initiative’s rival MediaVest, which is owned by Publicis Groupe. He was replaced in the role of MediaVest

Both Freeman and Mediabrands Ventures are more than just managing digital, an IPG rep tells paidContent. Beyond operating between the media agencies and the digital properties, Freeman will also manage the firm’s “specialized businesses,” which include Reprise Media (for search/social), Cadreon (audience demand platform), Ansible (mobile marketing), Orion Trading (media barter), Geomentum (hyper-local) and The Emerging Media Lab.

On top of that, Freeman is charged with increasing those businesses’ global scale. He’ll also be scouting for brands that IPG might want to acquire and invest in. On the digital side, Freeman will work closely with Mediabrands’ Chief Digital Officer Quentin George.

Freeman is best known as one of the founders of Omnicom’s seminal digital shop Tribal DDB. He left as CEO of Tribal DDB after 10 years to join Betawave (fka GoFish) in June ’08.

Betawave was not clear about why Freeman moved out of the CEO role in November. Aside from trying to trim its losses over the past year, the company has been keeping a fairly low profile, a contrast to the days when Freeman drew consistent industry attention when he was at Tribal DDB.

– What’s coming: As for what Mediabrands’ will be doing, the company’s online marketplace system will gather inventory from ad networks and ad exchanges. It will then cull data from sites visited by consumers and then match it to information in the marketer’s own customer database. The company will then devise a media plan around that data.

– Better late than…: Ad agencies and marketers are unable to content themselves with buying TV, newspaper and magazine ad space anymore. The economic meltdown has made that more than clear. And so, the realization that they have lost ground to companies like *Google*, *AOL*, *Yahoo* and *Microsoft* has been a bitter pill to swallow. While most agency execs tend to go out of their way to insist that there are no “frenemies” or “froes” when it comes to online advertising — especially since these shops have close partnerships with those internet companies — they know that in order to remain relevant, they have to step up and offer competing services. As Rob Norman, CEO of WPP’s Group M Interaction Worldwide shop, tells WSJ, “The ad-network business, we almost shouldn’t have allowed it to exist” adding that tech firms “got there first and dealt with the science before we did.”

The approach appears to differ from WPP’s somewhat, which has used its investment arm WPP Digital to acquire stakes in companies like Chinese rich media ad delivery outfit HDT Holdings Technologies, which is designed in part to give it a leg up in Asia, and game developer Realtime Worlds, which helps open up in-game ads as a new avenue for its clients’ spending. IPG will likely continue to make invests like its did in July, when it took a “strategic interest” in a company called Huge, which builds websites for marketers.