Initial public offerings may get all the attention, but when companies uncork secondary offerings, it's worth a close look at who is doing the selling.

Five Below Inc., the Center City-based retailer geared toward teens and preteens, last week said it had filed a registration statement for a follow-on offering of 8.56 million shares.

It's not unusual for a company to go back to the market with an offering within a year of going public. Five Below completed its initial public offering at a price of $17 per share July 24 and is currently one of The Inquirer's Philly 50 companies based on its market capitalization of more than $2 billion.

But I was surprised to see that this would be Five Below's second follow-on offering since the IPO. The first occurred in February when several of the company's largest shareholders sold 13.01 million shares at $35.65 per share.

Now three of those big shareholders intend to sell even more shares. Five Below won't receive any proceeds from either of the two secondary offerings.

Advent International Corp., a Boston private-equity firm that played a crucial role in funding Five Below pre-IPO, would sell 7.25 million shares, worth about $286 million based on Friday's closing price of $39.40.

Five Below cofounders David Schlessinger and Thomas G. Vellios also plan to sell more than 650,000 shares each, bringing each a windfall of more than $25 million.

John Zolidis, an equity analyst with Buckingham Research Group who has a neutral recommendation on the stock, said in his most recent investor note that he was "somewhat unimpressed" by Five Below's first-quarter sales and highlighted that "insiders continue to reduce positions fairly aggressively."

Are they ever.

Advent has cut its ownership stake from 62.5 percent of the outstanding shares before the IPO to 32.4 percent now. The new sale could shrink that to below 19 percent.

In October 2010, Advent invested $192.7 million in Five Below as the retailer began opening stores at a rapid clip.

Advent has already gotten its original investment back and more. It received proceeds of $380.7 million from the IPO and the January offering in addition to a special pre-IPO dividend of $62.2 million.

Add the $279 million expected from the second secondary offering and the $404 million worth of stock Advent still holds in Five Below, and that brings Advent's potential haul to more than $1.1 billion, or 5.8 times its original investment.

Executive chairman Schlessinger and CEO Vellios would trim their individual stakes in the company they founded in 2002 to 1.7 percent. But each is potentially a $100 million man.

So far, Schlessinger and Vellios have generated more than $39 million from share sales and dividends. Plus, they will continue to own shares worth at least $36 million.