By Louis Navellier of InvestorPlace

NEW 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.

Finally, let's look at Tower Semiconductor ( TSEM - Get Report). The stock is up 51% year-to-date, and is benefitting from a new tech boom as consumers continue to snatch up high-tech electronics even though other areas of spending are lagging. TSEM's first quarter earnings report topped expectations by 366%, and the semiconductor stock has seen a number of upwards revisions in recent weeks to next quarter's numbers. That means yet another impressive earnings surprise could be in the works as Tower Semiconductor keeps raising the bar. (P.S. I also highlighted Tower Semiconductor last week as a great penny stock to buy. It's up 7% in the last five trading days, proving I made a pretty good call!)

You get the idea from these three examples. As you can see, following the numbers provides the clearest reasons to buy stocks. That goes for big blue chips, but also for penny stocks too. And when you're searching for the best low-priced penny stocks to buy, having concrete numbers is invaluable.

To help you build a portfolio full of some growing penny stocks, check out these 24 picks that were all trading at less than $3 as of this morning's opening bell.

Hot Penny Stocks
*Click on Column Heads to Sort
Symbol Company Name Name Market Cap (M)
AEHR Aehr Test Systems Semiconductors $19.20
AIS Antares Pharma Health Care Equipment $143.40
ACLS Axcelis Technologies Semiconductors $179.00
CTHR Charles & Colvard Textiles and Apparel $55.40
CHCI Comstock Homebuilding Household Durables $34.30
EMMS Emmis Communications Media $85.70
HPOL Harris Interactive Inc. Media $62.50
IGOI iGo Inc. Computers & Peripherals $47.40
IMH IMPAC Mortgage Holdings Real Estate Investment Trusts $20.00
JOEZ Joe's Jeans Inc. Textiles and Apparel $140.80
LMLP LML Payment Systems Inc. IT Services $53.40
MGIC Magic Software Enterprises Software $67.00
MNDO MIND C.T.I. Ltd. Software $39.60
NENG Network Engines Inc. Communications Equipment $121.80
NEWT Newtek Business Services IT Services $47.10
OBCI Ocean Bio-Chem Inc. Household Products $15.90
PATK Patrick Industries Inc. Building Products $21.40
ROIAK Radio One Inc. Media $155.30
SLP Simulations Plus Inc. Software $34.20
SBSA Spanish Broadcasting System Media $110.50
TIII Tii Network Technologies Communications Equipment $21.90
TOF Tofutti Brands Inc. Food Products $14.70
TSEM Tower Semiconductor Ltd. Semiconductors $280.50
TTIL TTI Team Telecom Software $44.80

As of this writing, Louis Navellier did not own a position in any of these stocks in personal or client portfolios.

One of Wall Street's renowned growth investors, Louis Navellier is the editor of four investing newsletters: Emerging Growth (formerly known as MPT Review), Blue Chip Growth, Quantum Growth and Global Growth. His longest-running publication, Emerging Growth, has a track record of beating the market nearly 3 to 1. Navellier is the author of a BusinessWeek bestseller, "The Little Book That Makes You Rich," and the chairman and founder of Navellier & Associates, Inc.