By Louis Navellier of InvestorPlaceNEW YORK ( TheStreet) -- One of my favorite simple trading strategies for individual investors is to put your retirement money in a growing stock. That sounds pretty straightforward, but many investors quickly realize it's not as simple an investing strategy as it seems -- especially when it comes to finding hot penny stocks to buy now. After all, many of the big-name stocks to buy that you hear about every day are massive blue chips that have already seen their biggest growth. And some of the penny stocks that are small up-and-comers are aggressive, risky investments that could cost you everything. So how do you find growing stocks -- and specifically for smaller investors, the best penny stocks to buy? My advice to you is to look closely at the numbers. That means taking a hard look at earnings, sales and estimates for each investment you think is worthy of your retirement money. Take one of my favorite penny stocks to buy, Antares Pharma ( AIS). This penny stock is a leading health care equipment company that focuses on self-injection pharmaceutical products and technologies, and topical gel-based products. Though the company is not yet profitable, it has narrowed its loss in each of the last three quarters and has met or exceeded Wall Street expectations in each of these periods. That's a sign of positive momentum for this penny stock. Also worth noting is that investors everywhere have been snatching up AIS stock -- with shares up a whopping 57% year-to-date! (By the way, Antares was one of my favorite penny stocks to buy last week, too) Another great penny stock to buy is apparel manufacturer Joe's Jeans ( JOEZ). JOEZ stock is up more than 70% year-to-date thanks to strong earnings and sales. Despite its premium clothing with expensive prices, Joes Jeans has turned a quarterly profit in each of the last four periods -- including fourth-quarter profit that topped Wall Street estimates by 400%! That's earnings growth you can take to the bank, making JOEZ a great penny stock to buy now.