"Some of them have really turned into really good, solid businesses and they've really grown into their multiples," said Thomas Lee, co-founder and head of research at Fundstrat Global Advisors. He noted it's a good reminder that sometimes investors "can't be multiple sensitive."
Netflix is up more than 4,000 percent and Amazon.com is up more than 1,800 percent. Facebook wasn't publicly traded at the time of Google's IPO. Shares of the social network have gained more than 220 percent since its IPO on May 18, 2012.
"I don't think the FANG stocks are as important as they were in 2015," said Marc Chaikin, CEO of Chaikin Analytics. "They're doing well, which is always a comfort, but it is the average stock in the S&P that's propelling the market to new highs."
Over the last 12 years, the broad S&P 500 index is up nearly 100 percent to record highs. That's far less than Google's gains, but the historically high price-to-earnings ratio
for the index raises concerns for bull market skeptics.
Investors may also want to watch when growth stocks start losing momentum.
"You're not going to be able to buy (the outperformers) cheap," Hickey said. "They tend to have much more volatility. You have to have a pretty strong stomach to ride the wave."
And external pressures, such as slow global growth, can also weigh. Under pressure from the sluggish economic recovery and post-financial crisis regulation, financials dominate the S&P 500 laggards since Google's IPO. AIG is nearly 95 percent lower, Citigroup off nearly 90 percent and Bank of America 65 percent lower over that time.