Kiip, a firm that offers rewards for regular mobile app use, has announced that American Express Ventures has become an investor.

CEO Brian Wong (pictured) described Amex as “joining Kiip’s roster of strategic investors” in his blog, without specifying the size of its stake, or how much had been paid for it.

Kiip’s list of investors is growing. Existing luminaries include Verizon and ad giant Interpublic Group (IPG).

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

Recent customer wins for Kiip include working with Yahoo Japan on its mobile apps.