Much like Roku (ROKU) - Get Roku, Inc. Class A Report , shares of Snap Inc.  (SNAP) - Get Snap, Inc. Class A Report are tumbling Thursday thanks to an analyst downgrade.

Snap stock is tumbling 5.5% to $14.45 after analysts at Cowen downgraded the stock to underperform in "devastating" fashion, TheStreet's Jim Cramer said on CNBC's "Mad Dash" segment.

Analyst John Blackledge slashed his price target down to $11. Even after Thursday's 5.5% fall, his price target still implies 24% downside from current levels. Engagement on Snapchat is rising and while Blackledge forecasts rising ad spending, it will come at a cost. According to his survey work, Snap was one of the worst performers.

"They did an ad-buyer survey and they don't want it," Cramer said of Snapchat, adding that they instead want Instagram, a property of Facebook (FB) - Get Facebook, Inc. Class A Report .

Snap Inc CEO and co-founder Evan Spiegel

A whopping 96% of ad-buyers said they would prefer to advertise on Instagram Stories, a platform format Instagram essentially copied from Snapchat as the latter continued to gain traction. In less than a year, Instagram Stories had more daily users than all of Snapchat combined.

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Facebook's Instagram has acted as a weight on Snapchat, causing it many headaches when it comes to gaining momentum, reasoned Cramer, who also manages the Action Alerts PLUS charitable trust portfolio.

Advertisers are not flocking to Snap and while it's trying its hardest to break that trend, the demographic and platform simply aren't as fitting as Instagram. Blackledge acknowledges that the Snapchat platform is improving in terms of utilization and engagement, but its ROI, data and targeting did not rank well vs. the competition.

Facebook is a holding in Jim Cramer'sAction Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells FB?Learn more now.

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This article is commentary by an independent contributor. At the time of publication, the author had no positions in the stocks mentioned.