If you already own stock in Tesla Motors (NASDAQ:TSLA), you probably wish you owned more of it. Tesla stock is up more than 150% year to date. At the time of this writing, shares of the electric-vehicle maker were trading around $90 a pop. However, with as much as 86% of that upside occurring this month, is it too late for investors to get in on the action?

Who wants to know?

Whether or not Tesla stock remains a buy at its current valuation depends largely on how you invest. Buy and hold investors with an eye to the future and a stomach for volatility should see the stock climb higher from here in the years ahead. However, not all analysts share my enthusiasm for the stock's long-term growth potential.

Fellow Fool Sean Williams sees the stock's recent run-up as an opportunity to sell shares of Tesla short. He's certainly not alone. More than 37% of the company's free float remains sold short, even after the flood of good news out of the company this month. Still, it's important not to forget that the high short interest in Tesla stock was a major contributor to the steep rise in Tesla's value this month.

If that short squeeze has taught us anything, it's not to bet against Tesla or the company's outspoken CEO Elon Musk.

Valuing the big picture

On Wednesday, Musk gave investors yet another reason to get behind Tesla stock: He put more skin in the game. That's right, Musk said he would personally buy $100 million worth of Tesla stock, following the company's announcement Wednesday night that Tesla will raise additional funds through a stock and convertible-bond offering.

The takings will be used in part to pay back the $465 million owed to the Department of Energy. This means Tesla will not only be paying back its loan early, but it will also be doing so ahead of auto giants including Ford (NYSE:F) and Nissan -- although, to be fair, Tesla had the smallest DOE loan of the bunch. In fact, Ford borrowed a whopping $5.9 billion in green tech funding, while Nissan claimed $1.4 billion in taxpayer financing.

Ultimately, I think a secondary offering was the right move for Tesla as it cuts the political chains once and for all. Not to mention, Musk's additional investment in the company offers further proof that he is in Tesla stock for the long haul. For these reasons, I don't think it's too late for investors that can buy and hold shares of Tesla for the next five to 10 years. I certainly plan to add to my position going forward.