* Priceline and Hewlett-Packard both top expectations
* Groupon tumbles in premarket after forecasting loss
* Existing home sales data on tap, seen down 4.3 pct
* Futures up: Dow 36 pts, S&P 3.4 pts, Nasdaq 6.75
By Ryan Vlastelica
NEW YORK, Feb 21 U.S. stock index futures rose on Friday, indicating that a rally that lifted the S&P 500 close to record levels in the previous session could continue, following some strong results from technology companies.
* Market participants are looking ahead to data on January existing home sales, due at 10:00 a.m. EST (1500 GMT), which will give the latest glimpse into how the economy is faring as the U.S. Federal Reserve dials back its stimulus. Sales are seen falling 4.3 percent.
* Recent economic data has been mixed, with many metrics - including housing starts on Wednesday - indicating softness, though analysts have largely shrugged that off, pinning the weakness to frigid weather rather than softening fundamentals. Thursday's rally was partially fueled by a bullish read on factory activity, which seemed to support that view.
* Tech shares will be in focus a day after both Hewlett Packard Co and Priceline.com Inc reported results that topped expectations. Computer maker HP also raised its 2014 profit view, sending shares up 1.5 percent to $30.63 in premarket trading.
* Traders continued to watch the political situation in Ukraine, with EU mediators expecting an agreement between Ukraine's pro-European opposition and Russian-backed President Viktor Yanukovich, though the former was seeking last-minute changes to the deal. Geopolitical concerns may increase next week, where there will be few U.S. earnings and data releases to otherwise drive trading.
* S&P 500 futures rose 3.4 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures added 36 points and Nasdaq 100 futures rose 6.75 points.
* For the week, the Dow is down 0.1 percent, the S&P 500 is up less than 0.1 percent and the Nasdaq is up 0.6 percent. All three indexes are gunning for their third straight weekly gain.
* In company news, Groupon Inc slumped 14 percent to $8.80 in premarket trading a day after unexpectedly forecasting a quarterly loss, even as it reported revenue that was ahead of expectations.
* Pharmacy benefit manager Express Scripts Holding Co late Thursday forecast 2014 earnings in line with Wall Street expectations and said it expects long-term earnings growth of up to 20 percent per year.
* Tesla Motors Inc Chief Executive Elon Musk told Bloomberg TV that the company has had "conversations" with Apple Inc, responding to speculation that the iPhone and iPad maker had shown interest in the electric car company. Musk declined to describe the talks, though he said it was "very unlikely" that Tesla would be bought by any company.