Mark Mastrov net worth: Mark Mastrov is the founder of 24 Hour Fitness along with many other fitness businesses worldwide who has a net worth of $350 million. Mark Mastrov made his net worth through the many health and fitness clubs he founded in 1983 as 24 Hour Nautilus. He was born in Oakland, California and is still based in Northern California today. In January 2013 Mastrov made headlines as one of the potential buyers of The Sacramento Kings NBA franchise. Mastrov will face stiff competition to purchase the Kings from the Maloof family. 24 Hour Fitness was the first gym to be open, not surprisingly, 24 hours a day. Mark Mastrov attended Cal State University Hayward.