Reality Bites (FAANG) ...

Facebook Inc.s (FB - Get Report) $150 billion slide in after-hours trading hit tech media shares hard Thursday, with rivals falling sharply in pre-market trading on the back of concerns that new data privacy rules will hike costs and trim revenues in the second half of the year.

Facebook said second quarter costs rose more than 50% from last year to $7.4 billion, with that rate expected to hold over the course of the year, as its moves to arrest concern over the mis-use of customer data and broader privacy concerns linked to the Cambridge Analytica scandal that was revealed earlier this spring. At the same time, however, ad sales, which grew at the slowest rate in three years last quarter (to $13.2 billion) are expected to slow in the coming quarters as the impact of the European Union's General Data Protection Regulations (GDPR) takes its toll.

"Advertisers are still adapting to the changes, so it's early to know the longer-term impact," said Facebook COO Sheryl Kara Sandberg. "And things like GDPR and other privacy changes that may happen from us or may happen with regulation could make ads more relevant."

Action Alerts Plus holding Facebook shares were marked 20% lower in pre-market trading Thursday, indicating an opening bell price of $174.05 each, a move that would be the stock's biggest single-day decline since its May 2012 IPO and wipe out nearly all of its gains for the year.

This will be the worst gap down on earnings for a FAANG stock since Netflix $NFLX gapped down 25% on its October 2014 earnings, and that was before there even was a "FAANG"! From our Earnings Screener: https://t.co/vFFMKBVnKu pic.twitter.com/Ukn72t438C

— Bespoke (@bespokeinvest) July 26, 2018

Earlier this month Twitter Inc. (TWTR - Get Report) said it removed millions of fake or dormant accounts from its microblogging site, but rejected a Washington Post report that suggested the purge would impact its quarterly user metrics.  

"Most accounts we remove are not included in our reported metrics as they have not been active on the platform for 30 days or more, or we catch them at sign up and they are never counted," Twitter CFO Ned Segal said on Twitter last week. "If we removed 70M accounts from our reported metrics, you would hear directly from us."

Twitter which reports second quarter earnings Friday, was marked 3.6% lower in pre-market trading in New York, indicating an opening bell price of $42.61 each, a move that would still leave the stock with a year-to-date gain of around 80%.

Instant messaging rival Snap Inc. (SNAP - Get Report) was marked 3.4% lower at $12.98 while Google parent Alphabet Inc. (GOOGL - Get Report) , which was hit with the second of two multi-billion dollar fines by the European Commission in as many years last week, was marked 1.33% lower at $1,259.01 per share.

Google CEO Sundar Pichai told investors earlier this week that GDPR was "obviously something we've been working on for a long time well over 18 months, but the rollout just happened towards the end of second quarter. So, it's a bit early to us to say anything."

"But for us, it's been super important to get it right, and we've always been focused on user privacy. But, it's been a big change for a lot of our partners as well," he added. "And so, we are working closely with our partners and regulators and committed to doing it right, but it's too early to tell."

Amazon Inc. (AMZN - Get Report) , which reports after the bell Thursday, was marked 1.5% lower at $1,835.00 each.