New York : Wall Street didn't get the Facebook effect it was hoping for.

In a sign that the social networking giant may have already become a bellwether for its sector, shares of virtually every social media company sank Friday with Facebook's lacklustre debut on the stock market.

Anticipating that Facebook would have a big day, investors had loaded up on social media stocks in recent weeks.

Many backpedalled when Facebook's shares barely budged, rising just 23 cents, or less than 1 per cent, from the initial public offering price of $38.

"They were playing for a pop and didn't get it," said Michael Pachter of Wedbush Securities.

For instance, he said, "the guys who own Zynga were hoping it was going to go up to $9" from about $7.50 last week.

"When it didn't, they dumped it."

LinkedIn fell 6 per cent. Groupon was down 7 per cent. Yelp dropped 12 per cent. And Facebook's gaming partner Zynga took the worst hit of all, shedding more than 13 per cent of its value to close at $7.16.

At risk

"These social Internet companies trade together," said Herman Leung of Susquehanna Financial Group.

"So the market is probably asking, ‘Who else could be at risk?'"

The small group of social media companies all went public in the last 12 months.

Most of them have had a troubled tenure on the open market, disappointing investors and seeing heavy price drops.

The exception is LinkedIn, which enjoyed a more than 100 per cent spike on its own first day of trading and had experienced a steady rise over the last six months, nearly doubling since November.

But even the relatively solid shares of the professional social network were not immune to the side effects of Facebook's disappointing performance.

Like the other social media firms, shares of Zynga rose substantially in the days before Facebook's IPO.

Zynga's stock price had been up more than 10 per cent since Monday, but as Facebook went on the trading block, those gains vanished and the stock tumbled. Zynga dropped so quickly Friday that trading of its shares was halted twice.

A stock triggers a Nasdaq "circuit breaker" when it loses more than 10 per cent of its value within five minutes.

During the day, Zynga dipped to $6.40 a share, the lowest point it reached since it began trading in December.