Start Out was founded by Darren Spedale, an investment banker turned serial entrepreneur in Manhattan.  He came up with the idea for StartOut a year ago. Mr. Spedale, most recently a founder of A-List Global Media, a company that creates media and entertainment products for adolescents, noted that plenty of other groups had entrepreneurship associations — like Astia for women or TiE for South Asians.

“Why on earth isn’t there anything like this for the gay and lesbian community?” he remembers thinking. “It was a no-brainer.”

In fact, the last decade has seen a flowering of affinity groups for gays in business. M.B.A. candidates can get connected through Out for Business clubs at their universities and the annual Reaching Out conference, which brought more than 900 attendees to the Westin Peachtree Plaza in downtown Atlanta in October.

There are some 1.2 million gay-owned businesses in the United States and about 29,000 of them belong to local gay chambers of commerce, according to Justin G. Nelson, president and a founder of the National Gay and Lesbian Chamber of Commerce, which was organized in 2002 in Washington.

For too many years, Mr. Nelson said, the prevailing attitude among gay entrepreneurs in America was, “It’s O.K. for me to be gay, but I can’t do it in my business for fear that it will ruin my company.” That message, however, has evolved.