U.S. stocks were lower for the third straight week on Greece and European debt worries while Facebook’s (NasdaqGS: FB) highly anticipated IPO was a disappointment in the first day of trading Friday.

A social media ETF fell sharply on Friday amid the Facebook IPO. [Social Media ETF Down as Facebook Begins Trading]

Stepping back, U.S. stocks continue to move lower on speculation Greece will soon leave the euro. In Friday afternoon trading, the S&P 500 was down 4% for the week, the Dow slipped 3.4% and the Nasdaq Composite shed 4.8%.

Not surprisingly, the top ETF performers in the risk-off trade this week were volatility funds and Treasury bonds. The iShares Barclays 20+ Year Treasury Bond (NYSEArca: TLT) was set for a 4% weekly advance. [TLT Nears All-Time High as Yields Plunge]

Yields on the 10-year Treasury note are hovering near historic lows, suggesting investors are afraid of deflation and moving into safe havens.

There were also a few standouts in commodity ETFs this week with iPath Grains ETN (JJG) and U.S. Natural Gas (UNG) enjoying gains of more than 6%.

Conversely, other energy-related sector and country ETFs suffered the steepest declines this week. The worst performers included solar energy, uranium, coal, miners, Brazil and Russia.

The top three unleveraged ETFs this week were iPath Grains, PIMCO 25+ Year Zero Coupon Treasury (ZROZ) and U.S. Natural Gas.

The bottom three unleveraged ETFs this week were Guggenheim Solar Energy (TAN), Global X Uranium (URA) and Market Vectors Brazil Small-Cap (BRF) with losses of more than 12%.

In next week’s economic data, look for reports on new and existing home sales, durable goods orders and consumer sentiment.