What: Shares of Wayfair (NYSE:W) were were up 12.8% as of 11:00 a.m. EST Wednesday after the home furnishings online retailer reported a massive increase in sales in the first few days of the key holiday shopping season.

So what: Specifically, Wayfair says overall gross sales increased 109% year over year during the five-day peak shopping period between Thanksgiving and Cyber Monday. Growth in Direct Retail gross sales over the same period was even more impressive at 130%.

"The Thanksgiving holiday weekend is typically a busy, high volume period for Wayfair," added Wayfair CEO Niraj Shah. "We are continuing to see an industrywide shift to e-commerce that is especially evident during the peak retail season." 

Shah also elaborated that Wayfair is not only enjoying significant activity from new customers, but also strong purchasing from repeat customers.

Now what: But investors should know this growth likely isn't of the high-margin variety. Black Friday and Cyber Monday shoppers are generally out to find the best deals possible early in the season. As Wayfair's press release notes, "Wayfair customers took advantage of discounts over the long holiday weekend to stock up on items for entertaining and hosting friends and family." 

Then again, this isn't exactly new for Wayfair as it consciously forsakes bottom-line profitability in favor of building market share through top-line growth. Last quarter, for example, revenue grew 76.7% year over year to $594 million, and translated to an adjusted net loss of $0.13 per share. Both figures easily exceeded analysts' consensus expectations.

With that in mind, I think Wayfair investors are right to be encouraged by this strong start to the 2015 holiday shopping season. If the company can sustain this momentum as shoppers' appetites for early season discounts begins to fade, Wayfair's upcoming quarterly report should be very strong.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends Wayfair. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.