American Express is the latest strategic investor in mobile rewards network Kiip, joining companies like Verizon and Interpublic Group. The start-up didn’t disclose the amount of the AmEx investment or the size of the stake it was taking in Kiip.

In a blog post today, Kiip founder Brian Wong said the AmEx relationship would help the company’s “ecosystem” become stronger.

“As Kiip expands into more verticals, becoming even more integrated into peoples’ lives beyond gaming, we have evolved beyond media and advertising into a company that builds value into every moment,” he wrote.

It’s not hard to imagine American Express, which has partnered with the likes of Foursquare and Twitter on rewards and shopping-related programs, develop similar initiatives with Kiip. AmEx last year opened a venture capital office in Silicon Valley, led by Harshul Sanghi, who Wong worked with over the last year.

To date, the 3-year-old Kiip has raised over $15 million from investors including Hummer Winblad Venture Partners and True Ventures.