It was just over a month ago that social media management platform HootSuite picked up $20 million in a secondary investment round that valued the company at $200 million. Now we have heard from multiple sources that the company is looking to better than double that: HootSuite is in the process of raising a $50 million round at a $500 million valuation.

And what’s making this even more interesting are the investors that are being mentioned in connection with the round: HootSuite is looking to have discussions with Twitter, Facebook, LinkedIn and Google — a sign of how the surge in social media investments is also giving a lift to companies that are figuring out ways to harness that for third parties.

Facebook, Google, LinkedIn and Twitter were described by one source as all having a “great relationship” with HootSuite already, and that the company was looking to build a deal that would give them all “upside in Hootsuite’s success.”

We also reached out to HootSuite’s CEO Ryan Holmes, who wouldn’t comment directly on who might be investing but did confirm the $500 million valuation:

“At today’s run rate this would be a very fair valuation for investors, but we have yet to determine if we will bring in additional partners. That said, we have had quite a few inquiries,” he told me.

Facebook, Google, LinkedIn and Twitter’s networks already form the core of the HootSuite social media dashboard. Enterprises (and individuals) use that dashboard to monitor social media interaction across those networks, and they also use HootSuite for custom analytics and for executing and monitoring campaigns using other services like MailChimp, which HootSuite allows users to do through the web and via mobile apps. Customers include PepsiCo, Fox and the NBA among 3.5 million others.

You can see how that relationship could become even closer and be even more beneficial for Twitter, Facebook, LinkedIn and Google. Companies like Twitter and Facebook, built on consumer bases, need more inroads into the enterprise sector to further build out their businesses. LinkedIn, built on an enterprise customer base, needs to build out more products to serve them. And Google needs a lot more traffic and traction for its Google+ social media strategy.

A $50 million round would be a huge step up for HootSuite, which is profitable already but has reached that end at a relatively modest pace.

When HootSuite reported that OMERS Ventures, a Canadian VC firm, had taken a $20 million stake in the company in March, that was done through secondary purchases from existing shareholders, which included employees and also Blumberg Capital, Hearst Ventures, Geoff Entress and Millennium Technology Value Partners.

Before that $20 million deal, HootSuite had picked up investments worth $4.9 million: $3 million in debt and only $1.9 million capital investment.

Earlier this year HootSuite had reported an annual run-rate of $11 million in revenues. At the time it reported 140 employees and now expects to double that by the end of 2012.