A noted worrywart placed Shopify (NYSE:SHOP) back in its crosshairs last week, turning one of last year's biggest winners into one of last week's biggest losers. Shopify stock tumbled 12.1% last week after a Citron Research piece argued that the dot-com darling is headed for a fall in light of the profile harvesting scandal at Facebook (NASDAQ:FB)

Facebook concerns may or may not sting Shopify by limiting its total addressable market -- but just as we saw when Citron initially took jabs at Shopify's model in October -- creating doubts rocks the stock. Shopify bounced back the last time that Citron took a swing, but with the market and the stock's valuation more wobbly this time around it may not be so easy to bounce back.

Shopify's digital store platform on Facebook.

Image source: Shopify.

Shopping around

Shopify has had its share of ups and downs, but they've mostly been ups. Despite last week's setback the stock has still more than doubled over the past year. The stock made back all of the losses it suffered when Citron drew first blood in early October, but the recent correction is pushing it close to where it was at the time. Shopify kicks off this week trading just 7% higher than where it was the day before Citron's initial swing at Shopify. 

Citron began dissing Shopify six months ago, feeling that its growth in merchants -- 500,000 at the time and now more than 600,000 -- was largely the handiwork of aggressive affiliate marketing that Citron alleged was illegal. Shopify defended its business practices, and its stock price suggests that the market sided with the company over the bear. 

The new round of knocks centers on Facebook losing credibility, a more credible assault in light of recent events. Shopify leans heavily on Facebook for marketing its e-commerce solutions to aspiring entrepreneurs and as a platform that integrates with its own to let Facebook's more than 2 billion users shop easily from within the social networking hub. 

We'll naturally have to wait and see how this plays out. Citron's first shots proved hollow. It felt that back in October it was handing the Federal Trade Commission all of the evidence it needed to gun for Shopify. It never happened. Last week's shots will take time. Will merchant count suffer? Will transactions suffer?

Shopify seems to be in great shape at the moment. Revenue soared 71% in its latest quarter, a period that began just days before Citron's first bearish report. Shopify's 600,000 merchants rang up $9.1 billion in gross merchandise volume during the quarter. Growth should decelerate from here, but investors will need to keep an eye on Facebook's ability to bounce back from this data mining fiasco and how that impacts Shopify's fortunes.