Key Highlights

● Alphabet closed at $283.82, down from $324.89, erasing roughly $500 billion in market value.

● Eight of the S&P 500's eleven sectors rose on Thursday.

● Reddit and Pinterest fell sharply in after-hours trading on weak guidance.

● Meta rose, ending a five-session slide, but could not offset Alphabet's loss.

One stock's historic collapse was enough to turn an entire S&P 500 sector into Thursday's biggest loser by a wide margin.

The worst sector, by far

Eight of the S&P 500's eleven sectors rose on Thursday. Communication services was not among them. It finished as the worst performer in the index by a wide margin, falling far further than information technology or consumer discretionary, the other two decliners, according to market data.

The reason was simple: Alphabet (NASDAQ:GOOGL). The Google parent is one of the largest companies in the sector, and when a stock of that size suffers its worst day since its 2004 IPO, the whole group goes down with it.

Alphabet's historic drop

Alphabet's Class A shares closed at $283.82, down from $324.89, erasing roughly $500 billion in market value, according to market data. One report said that was the second-largest single-day wipeout on record, after Nvidia (NASDAQ:NVDA)'s $589 billion loss in January 2025. Another source noted the stock would have needed to close near $274.75 to break Nvidia's record.

The trigger was a Quarterly Report that missed on several fronts. Revenue of $127.58 billion trailed the $128.22 billion consensus, and Search revenue of $63.35 billion fell short of $64.96 billion. Adjusted Earnings of $2.67 a share lagged the $3.02 estimate, according to media reports. Free Cash Flow came in at negative $9.07 billion. One report said the results "reignited concerns over mounting AI costs."

The concentration problem

Thursday highlighted a structural feature of the communication services sector. A handful of giants, including Alphabet and Meta Platforms (NASDAQ:META), account for an outsized share of its value. That means a single earnings report can swing the entire group.

In fact, Meta rose on Thursday, ending a five-session slide after Pershing Square's Bill Ackman called the stock "incredibly undervalued" on television, according to market commentary. But Meta's gain was no match for Alphabet's loss.

The sector ETF told a similar story. The Communication Services Select Sector SPDR, XLC, was down at midday, according to market data, although its decline was smaller than the sector's final loss.

After hours, more pain

The evening brought more trouble for internet-media stocks. Reddit (NYSE:RDDT) fell sharply after hours after its fourth-quarter revenue guide of $1.00 billion to $1.03 billion missed the $1.05 billion consensus. Pinterest (NYSE:PINS) also tumbled in extended trading after missing on earnings and revenue and guiding below expectations. Roblox (NYSE:RBLX) slid on a soft revenue outlook and declining engagement metrics, according to market data.

A market that rotated

The broader market held up far better than communication services. The S&P 500 slipped 23.59 points to 7,720.39, and more than 400 of its members rose. Health care led all sectors, followed by real estate, consumer staples and utilities. The Russell 2000 gained 28.71 points to 2,859.22.

The Nasdaq Composite, heavy in Alphabet, fell 365.13 points to 26,184.72. "Money is rotating within the market rather than leaving it," one market strategist said.

What to watch

Communication services' outlook will hinge on whether Alphabet can stabilize. Investors will watch for any update on how quickly Google Cloud's $561 billion Backlog turns into revenue and cash, and whether Search growth recovers.

The after-hours declines in Reddit and Pinterest will be tested in Friday's regular session. Meta's rebound will also be worth watching, given its stock trading near the $625 price of its recent Equity offering. Thursday showed how much one stock can move a sector. The next few sessions will show whether that concentration works in the sector's favor again.