Here's a key takeaway from a national retail conference at the Convention Center this week: "Millennials are driving everything," said retail analyst Garrick Brown of DTZ.

Retail is a numbers game, and the demographic of individuals between 18 and 34 is now the largest consumer group in the United States, numbering about 85 million.

More of them shop online than any other group. Forty percent of male millennials say they were willing to buy everything online, and 32 percent of female millennials say the same.

Speaking at a panel of the Professional Retail Store Maintenance Association (PRSM), Brown said retailers are shifting resources from traditional brick-and-mortar stores to large warehouses and distribution centers that house merchandise and accommodate the growing online demand for goods.

Stores such as Walmart, Nordstrom, and Home Depot have moved in this direction, with the trend picking up this year. Brown said Amazon.com was the 800-pound gorilla "that everyone is chasing."

"Their monstrous distribution chain basically guarantees already 90 percent of the U.S. right now," he said. "It's next day without any extra cost. It's hard to match."

Some retailers, he said, were treading the fine line of combining traditional stores with their online counterparts - known in the retail industry as omni-channeling - to provide "a seamless experience" for the shopper.

"If a store doesn't carry [a consumer's] size that day, he or she is told by the store to order the item online to get it the next day with free delivery," Brown said. "The two work hand in hand."

Karen Shriner, director of facilities contract services for Rite Aid, said the pharmacy chain is developing ways to accommodate the millennial generation.

"We are expanding our social media network," said Shriner, who was among those in the audience listening to Brown. She took four employees - all millennials - to the conference.

Rite Aid has a Twitter account with nearly 50,000 followers.

"With our Wellness Loyalty Card, loyal customers can download their coupons onto their card," Shriner said. "It's all geared to millennials. They've pushed us in that direction. They are clearly the most tech-savvy."

The three-day conference, which ends Wednesday, attracted about 2,000 retailers and suppliers. Bryan Walker, president of the PRSM group, said the recession also slowed the expansion of new brick-and-mortar stores.

Star investor Daymond John, a regular on the TV show Shark Tank, gave the keynote address on Tuesday to a packed ballroom at the Convention Center.

"Everyone dreams about being in retail," John said, reflecting back to elementary school, when he sold customized pencils. "At the time, I didn't have aspirations or dreams, but over time I learned to set goals.

"It is always important to remember you are the brand," said John, the founder and chief executive officer of the retailer FUBU. "You have to know what you personally stand for."

With online shopping's growing dominance, Brown said, "it's all going to be about service in the new retail world and understanding and anticipating where the millennial consumer goes."

Stage Stores operates 854 department stores in 41 states, including Pennsylvania and New Jersey, under such brands as Peebles and Goody's. The company has an app and offers online next-day delivery of merchandise.

"While every company has to have a presence in the online world, it comes down to customer service," Stage Stores director of facility Stan Schmidt said.

"Our customer base is small-town U.S.A.," he said. "I tell my team: 'Don't think what you do doesn't impact the customer experience and the brand.'

"If the AC's not working, or the lighting's not working, the store isn't clean, or the carpet is stained, we are negatively impacting the customer experience."

sparmley@phillynews.com 215-854-4184 @SuzParmley