Leading tech analyst says one of the FANG stocks has not lived up to expectations

What's working: Still year of FANG

Out of the FANG stocks, Google's parent Alphabet is one that has not outperformed as expected, Mark Mahaney of RBC Capital Markets says.

"It's the stumper in the group," Mahaney said Friday on CNBC's "Squawk Box."

FANG is an acronym coined by CNBC's Jim Cramer for four of the most popular and best-performing tech stocks: Facebook, Amazon, Netflix and Google, now Alphabet.

Mahaney, lead internet analyst at RBC, said last year investors thought they were going to see a massive deceleration, but didn't.

"Why aren't margins doing a little bit better?" he said. "I think what they could do is take other bets generating about $4 billion a year in losses and prove that there is some revenue, some metric, some growth out there."

Mahaney's comments came as tech companies have been a driving force behind the market's recent rally. Some on Wall Street believe tax cuts and reduced regulations from President Donald Trump will give companies reason to spend more on cloud computing.

Disclosure: RBC Capital Markets makes a market in the securities of and Alphabet.