New York (CNN Business) Retailers like Toys "R" Us and Sears are vanishing. Planet Fitness is stepping in to fill the abandoned spaces they left behind.

Planet Fitness said this week that it will open 225 gyms this year. Some of those will be located in sites that Toys "R" Us or Sears once occupied, though the company declined to give a specific number.

The gym chain has been on a growth streak in recent years. It has more than 1,800 gyms in the United States, an uptick of about 60% compared to three years ago. Planet Fitness says it has the potential to reach 4,000 nationwide in the long run.

Planet Fitness PLNT The $10-a-month gym that pitches members on joining a "judgment free zone" with free pizza has posted more than 12 straight years of sales growth at gyms open at least a year. The company is one of the hottest stocks in retail: Shares ofhave climbed more than 400% over the past four years.

Investors are convinced that Planet Fitness has runway to grow by chasing the 80% of Americans who don't belong to a gym.

Retailers like Toys "R" Us, Sears and Sports Authority and others are vanishing. Planet Fitness is stepping in to fill the abandoned spaces they left behind.