SecondMarket was, in fact, approached by Mt. Gox some time last weekend.  Mark Karpeles approached Barry Silbert to solicit an acquisition offer, and it seems likely that Silbert, who had already committed privately to building a US-based exchange bitcoin exchange, jumped at the opportunity to explore the deal.

However, when the magnitude of the theft and potential fraud became free, Silbert and his team quickly pulled out of discussions, sent an email to all employees over the weekend banning them from buying or selling bitcoin indefinitely, and most likely reported the suspicious activity to the authorities.  As a regulated entity that probably signed a non-disclosure agreement before learning the full extent of the Mt. Gox damage, SecondMarket would have had no other choice, but to keep this out of the public eye, even if it was acting honestly behind the scenes.