Which startup was founded by Reid Hoffman?

Reid Hoffman co-founded LinkedIn.

Hoffman and a founding team drawn from his earlier technology work established LinkedIn in December 2002. The professional-networking service launched on May 5, 2003, with a goal different from that of general social networks: helping people represent their careers, maintain professional connections, find opportunities, and recruit talent.

The answer is sometimes simplified because LinkedIn had several founders and early team members, including Allen Blue, Eric Ly, Jean-Luc Vaillant, Lee Hower, and Konstantin Guericke. Reid Hoffman is nevertheless the canonical founder associated with the company. Myspace, Facebook, and Twitter belong to different social-networking histories and were not founded by Hoffman.

Hoffman brought experience from SocialNet and PayPal, and PayPal colleague Peter Thiel became an early LinkedIn investor. LinkedIn reached its first month of profitability in 2006 and held its initial public offering in 2011. Microsoft announced its acquisition of LinkedIn in 2016 for $26.2 billion, linking Hoffman’s startup to one of the largest technology acquisitions of that period.