The Samwer brothers of Germany have agreed to invest $10 million to $15 million in the hot social-networking site, a development which was first reported by Reuters and TechCrunch.

It feels like an awfully small amount to garner a key Facebook relationship in the important European market, so I would expect more to come.

A lot of people have doubted Facebook’s ability to raise more money after getting a lofty $15 billion valuation following a $240 million investment from Microsoft in October of 2007, which made the stakes very high.

And, indeed, the personal investment by the well-known European entrepreneurs comes after some time has passed since the last investment in Facebook in late November by Chinese investor Li Ka-shing of $60 million and possibly $60 million more, which was first reported here.

By coincidence, after meeting him at a dinner hosted by Accel Partners–a Facebook investor, in fact–in London in December, I am planning to visit with Marc Samwer next week in Berlin. Marc, with his brothers Alexander and Oliver, founded a German online auction site that was later sold to eBay and now run the European Founders Fund.

So, as they say over there: Ausgezeichnet!