Facebook (NASDAQ: FB) shares tumbled nearly 10 percent Monday to $20.79, after the highly influential business publication Barron’s ran a front page story in its weekend edition arguing that the stock was still overpriced and valuing it at $15 per share.

Barron’s compared Facebook to Google (NASDAQ: GOOG) and Apple (NASDAQ: AAPL), its most valuable and visible competitors in the technology sector, and argued that even accounting for the price premium inherent in a growth stock, shares of the social network remained vastly overvalued in comparison. Per the article:

"At its current quote, Facebook trades at 47 times projected 2012 profit of 48 cents a share and 36 times estimated 2013 earnings of 63 cents. Compare that with Google and Apple, two proven technology growth stories, which both trade for about 16 times estimated 2012 earnings. Facebook is valued at $61 billion, or $53 billion excluding its estimated $8 billion in cash. That's more than 10 times estimated 2012 revenue of $5 billion. Google trades for half that valuation."

Facebook has taken heat since its initial public offering in May, in which its main underwriter, Morgan Stanley (NYSE: MS), had to buy shares just to hold its list price of $38 at the close of its first day trading. The bottom would quickly fall out, as investors worried about the site’s disappointing growth in advertising revenue and perceived inability to successfully adapt its revenue streams to more of its users going mobile.

There are also concerns about Facebook’s need to pursue more aggressive—some might say invasive—methods to gather the type of comprehensive personal data it needs to monetize to grow as a business. A Sunday Financial Times story (paywalled at the FT site; syndicated by CNN) reported a new marketing plan by Facebook that raises privacy concerns:

"Datalogix has purchasing data from about 70m American households largely drawn from loyalty cards and programmes at more than 1,000 retailers, including grocers and drug stores. By matching email addresses or other identifying information associated with those cards against emails or information used to establish Facebook accounts, Datalogix can track whether people bought a product in a store after seeing an ad on Facebook."

Facebook’s precipitous Monday slide triggered a "circuit-breaker" mechanism on the NASDAQ. As the Wall Street Journal reports, this mechanism—allowing investors to sell a stock short if they have a buyer willing to pay more than the market price—is designed to prevent short sellers from sending the stock into a further downward spiral.

Read more of Neon Tommy’s coverage of Facebook here.

Read more of Neon Tommy’s coverage of Apple here.

Reach Executive Producer Matt Pressberg here.