Thursday's Winners & Losers: Google

Thornburg Mortgage(TMA Quote) failed to meet margin calls and received default notices due to the plummeting value of mortgage-related securities.

Thornburg said it failed to meet a $28 million margin call from JPMorgan Chase(JPM Quote), triggering a series of defaults on various lending agreements and increasing the probability of the company's demise. Thornburg shares were off 51.8% to $1.64.

Google(GOOG Quote) shares were down 3.4% as the company suffered a blow when a key senior executive moved over to rival Facebook.

Sheryl Sandberg, Google's vice president of global online sales, left the company to become Facebook's chief operating officer.

The stock was down $15.00 to $432.70 in afternoon trading and has lost 37.5% of its value since the start of the year.

Shares of Juniper Networks(JNPR Quote) were down after the company's board of directors approved a plan to spend $1 billion to repurchase common stock. The move is on top of earlier buyback plans to spend $2 billion in 2006 and 2007, of which $1.7 billion has been repurchased to date.

The board also approved a maintenance plan to issue shares to offset the dilution from shares issued related to the company's stock plan for employees.

The stock was was off $1.39, or 5.1%, to $25.83.

Reinsurance company CastlePoint Holdings(CPHL Quote) said fourth-quarter earnings fell 32% as the company booked losses on investments related to subprime mortgages. Net income dropped to $4.6 million from $6.8 million in the year-ago period. The stock was down 16% to $10.13.

Shares of Apple(AAPL Quote) were down after the company's show in Cupertino Thursday to discuss the future of the iPhone.

The company is expected to go after some of the lucrative corporate smartphone market now dominated by the BlackBerry by offering some new features, including the integration of Microsoft exchange email and a software developers kit to open the door for third-party applications.

The stock was down $3.56, or 2.9%, to $120.93.