That's what stocks do.
Capital Markets are not healthy today for instance people all over the world and in cities in the US all what better internet access but telecom companies can make more money with inferior service because there is no competition and customers make no choice.
Just a few companies have access to public markets, some company like Fitbit that just screws their customers and doesn't care about the future, they can cash out and get fuck you money even if their company incinerates the cash of investors. There are all the companies like hortonworks that have no differentiation, no patents, no moat, that get access to capital because of geographical bias that is no different morally from racism. If they were from Peoria they would be treated like dirt.
I will grant Y co that they give real mentoring, but their success has a lot to do with the fact that 99% of America is redlined, if you tried to do anything in any other city you would not have access to IPO money.
I hear that Y co peowould rather open an office in Singapore or Madras rather than Las Vegas or Chicago and if that is there attitude all the 99% can do is vote for Donald Trump or Bernie Sanders. If it all goes down in flames at least I can grow my own food you rich fucks go see what you can scavenge in a world that is half Palo alto and half mad max. Just listen for once.
The fact that there were dramatic declines in a few tech stocks makes traders worry that there may be similar earnings surprises in other tech stocks, so they dump tech stocks. If they see in a couple of weeks that these worries were unfounded, they might buy these stocks back again and the prices could go up.
According to the financial press, the stock market seems to be responding to global economic issues: the Chinese economy, weak oil prices, etc. Some fear a global economic slowdown. Since Google makes most of its money from advertising, its stock price would respond to concerns about the level of global economic activity. If people are buying less, businesses are selling less and advertising expenditures go down. (Same for Facebook Twitter, etc.)
If you believe that tech stocks are unfairly undervalued at this point, you might want to buy while the prices are low. But there are no guarantees that they won't go down even lower.