How Low Can You Go? Facebook Shares Dip Under $20.

What a gnarly week to be Facebook. First, a Silicon Valley developer takes a very public dig at you. Key executives announce their departures simultaneously. And now on Thursday, your stock tanks — hard.

Shares of Facebook dipped below $20, sinking to an all-time low of $19.82 per share in afternoon trading (it managed to claw its way back to $20.02 by the close, off 4 percent). That’s ugly, considering the stock was originally priced at $38 per share on its May 18 debut on the Nasdaq stock exchange.

Any of the previously mentioned factors could be affecting Wall Street’s wavering confidence in the social networking giant. Three key Facebook execs revealed that they were headed out the door on Wednesday: Ethan Beard of platform partnerships, and Katie Mitic and Jonathan Matus, both of platform marketing. Unfortunate timing, considering one of the biggest worries a company can have in its post-IPO period is a brain drain on top talent.

Or perhaps it’s the strange report that of Facebook’s 955-million-plus members, close to 80 million of those could be fake, duplicate or bot-controlled accounts.

Or it’s possible that even as Facebook hit its numbers in its first earnings call last week, growth and advertising just didn’t impress the Street enough to warrant confidence. To boot, shares of Zynga plummeted the day previous after the company reported a dismal earnings quarter. That could also affect Facebook, as the two companies have a symbiotic relationship through the revenue split on Zynga games hosted on the Facebook platform.

A note to day-one investors: Take a gander at this trending line, and look at how much you fought to get in at $38. For your sake, I hope you’re long on $FB$.