Groupon: Social media's Pets.com?

At this rate, Groupon (GRPN) may never get back to a $6 billion market value. That number, in case you forgot, is what Google (GOOG) reportedly offered to buy Groupon for back in 2010. Groupon went public instead.

Oops.

Shares of Groupon plunged 23% Tuesday to a new all-time low after the company reported revenues that missed forecasts and sluggish guidance after the bell Monday. Groupon's market value is now below $4 billion. The stock has plummeted 72% year-to-date.

Is Groupon shaping up to be the next Pets.com? Maybe not. But its long-term viability is coming into question. And investors clearly have soured on every social media stock not named LinkedIn (LNKD). Facebook (FB) and Zynga (ZNGA) have taken their lumps. So have Pandora (P) and Angie's List (ANGI).

Even reviews site Yelp (YELP), which had been holding up better than other social stocks, took a nasty tumble Monday on the news that Google was buying travel publisher Frommer's from John Wiley (JWA). Investors feared what a combination of Google's Zagat brand and Frommer's could mean for Yelp ... as well as TripAdvisor (TRIP). It just goes to show that any of the upstart social stocks (even Facebook) could face brutal competition from giants like Google -- which have a lot more cash at their disposal to throw at new projects. For more on Groupon and the social media slide, check out today's Buzz video below.