When founder Anthony Casalena first started Squarespace in 2003, he had one investment: $20,000 from his dad. At the time, it was just enough money to get a few servers for his web publishing startup.

Anthony Casalena launched Squarespace in 2004 spurred by the inability “to find a way to elegantly publish his personal website.” Since then, the New York City-based company has grown to a team of 580 ...