The Verizon and Salesforce-backed push notification service has boosted its series D round to $37.1m after closing a second tranche.

Urban Airship, a US-based developer of push notification services for smartphones backed by investors including Verizon and Salesforce.com, has raised $12.1m in its series D follow-on round.

Venture capital firms True Ventures, Foundry Group and August Capital provided the new capital as repeat investors after Urban raised an initial $25m in February 2013 from investors including telecommunications firm Verizon Communications and enterprise software developer Salesforce.

Brett Caine, CEO and president of Urban Airship, said: “Having just come on board Urban…