Simon Property Group, the Indiana-based company that owns the King of Prussia Mall and Philadelphia Mills in the Northeast, is joining Conshohocken-based Michael Rubin, who owns online sports merchandise leader Fanatics, in a “digital value shopping” venture to boost store sales through online specials and discounts.

The website, ShopPremiumOutlets.com, has attracted 14 million visitors since a beta version went online in March, according to Simon. The new portal will be managed by Rubin’s Rue Gilt Groupe, formed last year to combine Rubin’s Boston-based Rue La La high-end retail discount service with member-shopping service Gilt, which Rubin bought from Saks Fifth Avenue owner Hudson’s Bay Co. as its sales declined.

The new venture will employ about 900 people, including a Kentucky warehouse operation. At the time of its creation last year, Rue Gilt employed about 750 and claimed sales of about $1 billion.

Simon pledged to help market the venture to the customers at the hundreds of big stores in its properties. The companies said they would pool information on 35 million combined customers.

Rubin, a partner in the 76ers, founded the former GSI Commerce, which managed online sales for retailers competing with Amazon.com. He sold it to eBay in 2011 for $2.5 billion.

He is known in Philadelphia for his advocacy of the rapper Meek Mill, who was freed from prison on parole violation charges after Rubin and other defenders hired a legal, investigative, and public relations team, and has gone on to help lead Reform Alliance, a criminal justice advocacy group. In 2017, Rubin bought the struggling Majestic sports-uniform factory near Easton, Pa.

Rubin’s companies have competed with mall chains such as Simon and with online and media-based retailers such as the West Chester-based Qurate Retail Group, owner of QVC and Zulily.

David Simon, chairman and CEO of Simon Property Group, in a statement called the seven-month ShopPremiumOutlet.com test successful and said the online sales specials complemented the company’s stores. “We believe online value shopping presents a tremendous business opportunity for Simon,” he added.

Online value shopping is “a massive opportunity ready for the next disruptor,” Rubin said. He said Rue Gilt will use the partnership “to quickly surpass $1 billion in sales.”

“We are excited to partner with Simon on this innovative e-commerce property,” said Mark McWeeny, CEO of Rue Gilt. “Our expertise in e-commerce, data science, curation, and customer experience was the foundation for this partnership.”