Shares of Penn National Gaming Inc. PENN, -7.21% slumped 5.1% in premarket trading Thursday, after the online gaming company said it has launched a public offering of 14 million shares of its common stock.

The offering represents about 10.2% of the approximately 137.6 million shares outstanding.

Based on Wednesday's stock closing price of $69.00, 14 million shares would be valued at $202.9 million.

Penn said it plans to grant the underwriters of the offering options to buy up to an additional 2.1 million shares.

The company expects to use the proceeds from the offering for general corporate purposes.

The stock has soared 170% year to date through Wednesday, while the S&P 500 SPX, -2.37% has gained 0.2%.