Roku plunges after providing a weak sales forecast

• Roku beat on earnings, but missed on its forecast.
• The stock has surged since its IPO last year, but plunged Thursday.

Roku shares plunged 18 percent Thursday, a day after the maker of digital streaming devices provided a revenue estimate that trailed analysts' estimates.

Roku said sales in the first quarter will be $120 million to $130 million, falling short of the $131.7 million average estimate of analysts surveyed by Thomson Reuters.

Here's what Roku reported for the fourth quarter:

• Revenue: $188.3 million vs. $182.5 million estimate, according to Thomson Reuters
• EPS: 6 cents (not comparable with estimate of 10 cent loss)

Investors have piled into Roku shares since the company's IPO in September, with the stock more than tripling to $51.10 as of Wednesday's close. While Roku is seeing explosive growth from its platform — the smart TV software and ads business — competition from Amazon, Google and Apple is increasing.