NEW YORK ( TheStreet) - The "Triple Net" real estate investment trust sector has been growing like a weed this summer as the biggest companies in this area -- Realty Income ( O) and American Realty Capital Properties ( ARCP) -- make deal after deal.But the smaller players are growing, too, and deserve some attention. In particular, three smaller Triple Net REITs are flying under the radar. Investors may want to consider them. (Triple Net REITs, a relatively new area, refer to property owners whose tenants agree to pay real estate taxes, building insurance and maintenance costs (the three nets), in addition to rent and utilities.) Gramercy Property Trust ( GPT) is a small-cap REIT ($277 million market cap) that invests in office and industrial assets. The company's real estate valuation is about $463 million based on a cap rate (net income divided by purchase price) of 7%, and its portfolio consists of 1.6 million square feet in office space, 1.75 million in industrial space, and several truck terminal properties. Gramercy is the smallest Triple Net REIT in the Triple Net or Industrial sectors, and it doesn't pay a dividend, which is unusual for a Triple Net REIT. Still, Gramercy has been one of the top performing equity REITs this year. Year-to-date, it has returned over 58%, and based on its recent accelerated growth, I expect a dividend will come soon. I think the stock - trading around $4.70 -- is undervalued, and could grow by 25% this year, based on a peer multiple of 16 times price/funds from operation. Agree Realty Corporation ( ADC) was founded in 1971 by Chairman and CEO Richard Agree, and it has been public since 1994. With a market cap of $407 million, it's considered a small-cap REIT with 109 properties -- 100 single-tenant and nine shopping centers -- in its portfolio and over 3.3 million square feet in 27 states. Agree recently announced a first-quarter dividend of 41 a cents a share, up from 40 cents previously. It is fairly valued with a P/FFO multiple of 14.7x. and carries a healthy 5.33% dividend yield. Finally, in May, I wrote about Chambers Street Group ( CSG) when the REIT listed shares on the New York Stock Exchange. With a portfolio of 129 properties and 34 million square feet, I recommended that investors consider buying shares in the low $9s ($9-$9.25). Since the listing, Chambers Street has dropped below $9, a sound entry point. The market cap is about $2.1 billion, and the P/FFO valuation of 15.1x is in the fair value range.