The Los Angeles Business Journal’s index of largest local public companies dropped more than 9 percent for the week ended Aug. 5 following the biggest stock market plunge in three years.

The weighted LABJ index ended the week down 9.5 percent to 111.15, with decliners outpacing gainers 145 to 22 and 13 companies unchanged.

Shares of CyberDefender Corp. fell nearly 34 percent to 60 cents. The Los Angeles Internet security software company said that Chief Executive Gary Guseinov had resigned and some product development employees had been laid off.

Most of the other big movers were related to earnings announcements. K-Swiss Inc. sank 32 percent $7.25. The Westlake Village athletic footwear maker reported a wider-than-expected second quarter loss despite higher revenue, and lowered its guidance for the year.

A weak fiscal first quarter earnings report also hurt RealD Inc., a Beverly Hills maker of 3-D theater projection equipment. Shares fell 28 percent to $13.30.

THQ Inc. lost 21 percent to close at $2.15. The Agoura Hills video-game publisher reported a disappointing fiscal first quarter loss.

The biggest gainer was Meruelo Maddux Properties Inc., which jumped 96 percent to $4.90. The Los Angeles owner of office properties exited Chapter 11, completed a five-to-one reverse stock split and named a new chief executive.

Stamps.com Inc. which rose 27 percent to $17.41. The Los Angeles provider of Internet-based postage services reported better-than-expected second quarter earnings.

Staar Surgical Co. jumped more than 12 percent to $5.33. The Monrovia maker of implantable eye lens reported its second consecutive quarter of profitability – the first time that’s happened since 1999.