Nov 24 (Reuters) - Exchange-traded funds (ETFs) tracking U.S. retailers moved higher in shortened trading hours on Black Friday, outpacing broader market indexes.

While the S&P 500 index ended little changed, the Amplify Online Retail ETF climbed 0.4% and the broader SPDR S&P Retail ETF gained about 0.7%. Both continued to rise in after-hours trading.

Retailers and analysts have warned of a lackluster outlook for this year's holiday shopping season.

While the National Retail Federation, an organization representing large retailers, expects overall U.S. holiday to hit a new record of about $967 billion in 2023, that 3% to 4% gain from 2022 would still be smallest since 2019.

Retailers like Gap, Walmart and Best Buy have voiced caution about the outlook for the holidays and beyond.

"I believe that some forecasts have been distorted by the recently ended United Auto Workers and Hollywood SAG-AFTRA actor strikes, which caused a pullback in spending amongst various large pockets across the country," said Michael Ashley Schulman, chief investment officer at Running Point Capital.

The SPDR S&P Retail ETF, which has net assets of $396.6 million, recorded weekly outflows of $115.6 in the week ended on Wednesday, according to data from Lipper. That was the largest drop in a month.

Still, the bulk of 2023 returns for investors in U.S. retail ETFs have come in recent weeks. The SPDR fund is up 4.98% since Sept. 30, but only 5.69% throughout 2023. The VanEck Retail ETF has generated half of its 12.8% year-to-date gains in the last two months.

ETF investors "have been alarmed by retailers warning of cautionary, weak, or uneven consumer demand," Schulman added.

But Thomas Hayes, chair at Great Hill Capital LLC in New York, anticipates better-than-expected gains in retail stocks this holiday season.

"Expectations are very low, which sets the stage for a positive upside surprise," he said. (Reporting by Suzanne McGee; Editing by Lananh Nguyen and Josie Kao)