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Tuesday was a big day for Facebook (FB) as 13F filings showed hedge fund heavyweights Moore Capital, George Soros, Steven A. Cohen's SAC
Capital and Tiger Management took positions ranging from 15,000 shares to 2 million shares.

Apparently, none of these presumably savvy investors were dissuaded by the coming lockup expiration that ultimately could bring nearly 2 billion additional shares onto the market between now and next May. Given Facebook issued 'just' 421 million shares at its ill-fated IPO in May, the potential for that huge new supply of stock is reason for caution, says one of the more bullish sell-side analysts who follow the stock.

Ken Sena, managing director at Evercore Partners, has a $34 price target on Facebook, citing its long-term potential to unlock the trove of data it has on its roughly 1 billion users. At about $4 per user, advertisers are currently paying Facebook a much lower rate than the $30 per user Google (GOOG) receives.

Sena believes that spread will narrow and is "fairly bullish" Facebook will, over time, be able to unlock the value of that data.

Still, he thinks the stock "goes lower before it goes higher," largely because of the lockup expiration, which begins Thursday when insiders are able to sell up to 271 million shares. Subsequent expirations in October, November and December will allow CEO Mark Zuckerberg and other Facebook employees to sell more than 1.2 billion shares. The final lockup expires next May, when late-stage investors affiliated with Russian billionaire Yuri Milner, DST Global and Mail.ru Group Inc. get a chance to cash out.

The potential silver lining here is that this lockup expiration is widely know and thus already "priced in" the stock.

Sena believes that's likely but "it's still probably safe…to wait until you see some of that supply hit the market and see what kind of demand is there on the other end given there are certain fundamental challenges the company is facing right now."

Beyond the sheer supply of stock is the fact that many of the pre-public Facebook investors, such as Fidelity and T. Rowe Price, were also early investors in Zynga (ZNGA) and Groupon (GRPN), whose post-IPO performances have been even worse than Facebook's. (See: 5 Best, Worst IPOs of Past Year: Groupon Slumps, Michael Kors Soars)

"For owners who didn't distribute on Groupon or Zynga because the price was too low, they're sitting back now and regretting it," he says. "Even if you have that long-term view [of Facebook] and think the value is there...if you believe everyone around you is going to be selling it and your value is going to go lower, you're likely going to want to sell it too."

But again, he's a long-term bull and some savvy investors have been buying the stock ahead of expiration, a rare bit of good news for suffering Facebook shareholders.