Snap Inc. had its first down day in the stock market since going public on Thursday.

Shares of the parent company of Snapchat fell 12% in trading on Monday to as low as $23.79, below the opening price of $24 a share. They were about 16% lower than their high after the initial public offering.

Even though there was huge demand for Snap's shares, making it the largest tech IPO since Alibaba in 2014, none of the seven analysts who cover Snap rate it a "Buy." Analysts who advise investors to sell are warning about strong competition from Facebook and Twitter and slow user growth.

Over the weekend, Barron's magazine said the company's shares could be cut in half.

It's still very early days for the stock, which may test some early investors' patience. The drop below $24 effectively erases gains for those who bought as the stock went public. The IPO priced at $17 a share.