Google Inc. posted a 3% increase in first-quarter net income despite a continuing decline in how much advertisers pay per click, as users shift to smartphones and tablets.

The Internet-search giant said revenue rose 19% to $15.4 billion. Analysts had projected revenue of $15.54 billion on that basis, according to Thomson Reuters.

Investors were disappointed by Google's financial figures, sending its shares down 5% in after-hours trading.

Google reported net income of $3.45 billion, or $5.04 per share, compared with earnings in the year-earlier period of $3.35 billion, or $4.97 per share. Excluding stock-based compensation and other items, Google said earnings were $6.27 per share, below the average analyst estimate of $6.41 a share, according to Thomson Reuters.

Advertising revenue was driven by more clicks on advertiser links next to Google's search results, which increased 26% from the prior year. At the same time, the amount Google gets paid per click fell 9% compared with the prior year, continuing a trend as a higher percentage of searches occur on smartphones, where Google's clicks are less valuable.

The smaller screens and limited bandwidth of smartphones make them a less-appealing tool than desktop computers for consumers looking to buy products or services online. Marketers that work with digital ad firm Rimm Kaufman Group paid about 60% less for smartphone clicks than desktop clicks in the first quarter in order to generate an equivalent payback.

Write to Rolfe Winkler at rolfe.winkler@wsj.com and John Kell at john.kell@wsj.com

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