Stocks in the U.S. continued their decline Monday as investors continued a heavy sell-off of high-growth stocks.

Investors are looking forward to first quarter earnings reports and many analysts are remaining negative about these coming reports.

The NASDAQ Composite, a tech-heavy index, sunk over 1 percent to 4,079.75, which is below its 100-day moving average. Over the past three sessions, the index has lost 4.6%. This is the worst three day slide for the NASDAQ since November 2011.

Besides the NASDAQ, the Dow Jones Industrial Average (-1.02 percent) and the S&P 500 (-1.08 percent) also sunk. Additionaly, financial stocks were hit especially hard Monday.

There isn't much economic data to be released this week, so investors will focus on earnings reports such as Alcoa Inc. The aluminum producer reports Tuesday after the closing bell.

Some analysts are concerned about the declines of stocks and the heavy amount of selling that began Friday.

"The weakness has carried over from Friday. It is hard to imagine how the S&P 500 went from a new all-time high to   down on the year in just two days, but it happened. The momentum names and technology names were the first to crack, now we are seeing signs that weakness is moving to the overall market," senior technical strategist Ryan Detrick told Marketwatch.

But other analysts are saying these warnings are going a little overboard. In fact, this is the 16th quarter in a row where investors have been warned about earnings.

Most Internet companies have been taking a hit lately as well.

Chinese search engine Baidu Inc. continued to fall Monday, losing 2.7 percent. Baidu was trading as high as $174.18 in March, Monday the stock closed at $143.50.

While Baidu fell, Facebook (+0.32 percent) struggled to make a small gain Monday. The social media giant has lost 18 percent since March 10. 

While the financial sector and Internet stocks struggled Monday, one pharmaceutical was able to make big gains after agreeing to be purchased.

Questcor Pharmaceuticals gained 16 percent after agreeing to be bought out by Mallinckrodt. The two companies will be a joint company. The deal is said to be worth $5.6 billion.