Viadeo, the professional social network that competes against LinkedIn with about 40 million users, announced it has acquired Dutch startup Soocial for an amount equal to ‘multiple hundreds of thousands of euros,’ according to a report by a French media outlet. Soocial’s staff will now be working on fleshing out Viadeo’s platform, though the main reason behind the acquisition is Soocial’s syncing functionality.

“Contact and synchronization management can quickly become a nightmare for a professional who must often juggle multiple formats of business cards and various electronic devices,” said Dan Serfaty, CEO and founder of Viadeo. “We are very pleased to announce the Soocial acquisition, which will provide  our 40 million members worldwide with the best technology to manage their contacts.”

Once the new functionality has been rolled out, Viadeo account holders will be able to sync their contacts across machines, mobile devices and email addresses.

Viadeo’s user base has grown by 5 million or so in a period of just two months, when we reported the release of an open API aimed at allowing developers to integrate Viadeo components into their sites. The company is seeing a lot of growth, and increase in international traffic can be credited to a sizable portion of it. Last week Tianji, a Chinese social network for business user that was bought out by Viadeo, said it expects 18 million users by the end of 2012 compared to its current 8 million.

While Viadeo is expanding LinkedIn is also making gains. Forbes put a price of $42.87 on the network’s stock yesterday, and stood behind the share’s value by citing several drivers that are increasing the network’s popularity. Among them is an effort to attract small businesses in order to increase the number of paying users rather than their individual value.