No doubt about it: Longtime activist investor Carl Icahn knows a thing or two about spotting good opportunities. Icahn's investment fund ended last year up 31%, about the same as the U.S. market. Not bad in a year when many hedge funds underperformed. Investors were also duly impressed with Icahn's stake in high-flyers like Netflix, which jumped a whopping 283% last year and netted his firm a small fortune.

The iconic investor's success in 2013 catapulted the stock price of his publicly traded investment vehicle, Icahn Enterprises (IEP 1.53%), to a nearly 160% increase last year. And that brings us to Icahn's latest pet project, Apple (AAPL 1.27%). As his tweet late last month after adding another $500 million in iShares reminded us, Icahn owns a lot of Apple stock: more than $3 billion worth, based on yesterday's close. And his seemingly unending tweets, interviews, and requests for increasing Apple's stock buyback program -- even beyond the recent $14 billion in shares CEO Tim Cook recently bought back -- makes it clear how he'd try to boost its share price. But suggesting that Apple should trade anywhere near $1,245 a share, as Icahn recently did via, what else, a tweet, is over the top.

Icahn's logic
In yet another Twitter missive yesterday, Icahn compared Apple to Google's (GOOGL 0.55%) valuation, tweeting:

$GOOG @ 19x2014 est operating profit. At same multiple $AAPL=$1,245 per share. Ridiculous. Keep buying Tim! You still have $145 billion cash.

Of course, as iFans know, Apple closed yesterday up $7.17 a share, to $519.68,  bout where its stock price has meandered for a while now. So $1,245 per share is quite a leap, even for Icahn.

In his open letter to Apple shareholders late last month, Icahn listed several reasons he thinks Apple is undervalued -- after reminding shareholders of his many investment successes-and it's difficult to argue with many of his assertions. Apple, as Icahn pointed out, was trading over 70% below the average price-to-earnings multiple of the S&P 500. Icahn also cited Apple's strong cash position and earnings estimates of nearly $40 billion this year as upsides.

Of course, expected earnings in 2014 and $130 billion in net cash, as per Icahn's open letter, are the impetus for his continued calls for Cook to buy back more and more stock. With its shareholder meeting scheduled for Feb. 28, you can expect to hear more Apple stock buyback chatter from Icahn in the coming days and weeks.

So why isn't Apple trading like Google?
Both Apple and its smartphone OS nemesis Google generate revenues and profits that are the envy of their peers. However, there are distinctions between Apple and Google -- some tangible, some intangible -- that have contributed to the moving of their respective stock prices in opposite directions. Apple's woes are well documented: margin concerns as the mobile industry becomes even more hyper-competitive, its reliance on iPhones for the vast majority of its profits, and a lack of innovative, new products.

The problem in comparing Apple and Google's stock price today is that the former's shortcomings are all Google strengths. With its diversity of products including search, its own and partner's websites, and world-leading mobile OS Android driving ad revenues, Google shareholders aren't worried about margins or revenue diversification. As for innovation; self-driving cars, Fiber Internet, and Glass, are just a few of the cutting-edge technologies that puts Google in a class by itself.

Final Foolish thoughts
One look at Icahn's sale of Netflix stock last year -- though he still holds a good-sized chunk -- should be telling for Apple investors. Icahn let the world know he bought Netflix, hyped it to no end, and then sold it after its incredible run-up for an $825 million gain. In short, Icahn is the yin to buy-and-hold guru Warren Buffett's yang.

Icahn is interested in gains, plain and simple, and who can blame him? And if generating those investment gains means hyping a stock via traditional and social media outlets, Icahn's your guy. But valuing Apple at $1,245 a share based on a strong cash position and rumored new products doesn't fly. Hype, good or bad, unfortunately can have a short-term impact on stock prices. The problem with Icahn's public relations campaign for all things Apple is once he gets his stock price pop, he's gone. Not exactly a model for long-term investors.