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SAN FRANCISCO -- Wall Street doesn’t like Facebook’s $19-billion deal to buy mobile messaging company WhatsApp.

Shares slid about 2% to $66.68 in early trading Thursday, erasing a few billion dollars in market value.

“The $19-billion price tag is an unfathomable price based on any near-term multiple,” said Macquarie Securities analyst Ben Schachter.

As for the longer term? “We won’t know for some time if the price paid actually looks more reasonable,” he said.

The reaction from Wall Street echoes Facebook’s $1-billion acquisition of photo-sharing service Instagram.

At the time analysts thought Facebook had paid too steep a price for the tiny company.

“However, in hindsight, the Instagram deal at $1 billion now looks very good, despite the initial criticism,” Schachter said.  “That is not to say that the WhatsApp deal will turn out to be a home run, but the lofty valuation could end up looking more attractive over time.”

Facebook’s deal to buy WhatsApp is larger than any other acquisition in recent memory, including Microsoft’s $8.5-billion purchase of Skype.

Some analysts say they see the strategic value of the acquisition. J.P. Morgan Doug Anmuth said WhatsApp would help strengthen Facebook’s position in mobile messaging, international markets and with teens.

“We do believe WhatsApp is one of the few networks on the path to reaching over 1 billion users over the next few years, making it an extremely attractive asset over time,” he said in a research report. “Worldwide smartphone adoption is expected to reach 5 billion users over the next several years and WhatsApp, as the current global leader in mobile messaging, is quickly becoming a core application on mobile.”

But Pivotal Research Group analyst Brian Wieser downgraded Facebook to a “hold” with a new price target of $66 anyway.

“While we see strategic merit, the acquisition is difficult to justify on metrics we use to value Facebook,” he said.

WhatsApp co-founder and Chief Executive Jan Koum said Wednesday that WhatsApp would remain focused on growing its user ranks, not building a business.

That statement may have made some on Wall Street nervous. Facebook Chief Financial Officer David Ebersman tried to calm nerves by saying that over time WhatsApp would deliver “significant returns for shareholders.”

But to justify the $19-billion price tag, WhatsApp would need to generate about $1 billion in annual cash flow by 2018, Wieser said.

“However, few data points to support such an assumption were provided by the company, as evidently few are available,” he said.

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