Could the stock market be headed for trouble?

New reports suggest just half a dozen companies are fueling much of the gains on the Nasdaq, and so far falling stocks outpace rising stocks, which has been a precursor to previous downturns.

But while analysts and investors are raising concerns about the larger market, Facebook — one of the few companies driving gains — has them feeling optimistic after this week’s earnings report. The numbers certainly impress Wall Street.

Facebook’s margins are high, people are spending more time hanging out on the site and it boasts 1.4 billion users on average a month.

RBC analyst Mark Mahaney says that’s jaw-dropping. “For context, there are more people on Facebook on a monthly basis than live in China. It’s a massive platform,” he says.

The future appears bright for a company valued at more than $250 billion, which helps explain why it’s one of Wall Street’s spark plugs.

Another growth area for the company is advertising. Facebook hauled in $3.8 billion, three-quarters coming from mobile.

Brian Blau is research director at Gartner. “Advertisers want to put their ads in front of Facebook users. And I think that we continue to see that as Facebook presses down and attracts more advertisers in local communities,” he says.

Blau says Facebook may have maxed out growth here in the U.S. and much of Europe.

One way to keep humming along is to find a way to make more off advertising that doesn’t turn users off.