In a year heralding the landmark initial public offering of Facebook Inc., share sales got off to a slow start.

While more companies tapped equity markets in March, IPOs globally raised $16.2 billion in the first quarter, the least since 2009, data compiled by Bloomberg show. That kept the backlog of deals in the U.S. near the highest in more than a decade, according to Renaissance Capital LLC.

Investors are still smarting after losing money last year on IPOs from Groupon Inc. to Glencore International Plc, even as U.S. stock market volatility fell to an almost five-year low in the quarter and set the stage for a rebound. Share sales in the U.S., Asia and Europe picked up in recent weeks, led by Allison Transmission Holdings Inc. and Dutch cable-television operator Ziggo NV.