Whisper, a mobile app that allows people to communicate anonymously, has raised $21 million in new funds from a group of venture capitalists led by Sequoia Capital general partner Roelof Botha.

Botha is to join Whisper’s board.

GigaOm revealed in July that Whisper, which provides an easy way for users to add text to images and share them without revealing their identity, had raised a large Series B round of funding (rumoured to be about $15 million, according to its Silicon Valley sources).

The company, co-founded by Michael Heyward and Brad Brooks, raised $3 million in Series A funding from LightSpeed Venture Partners, Trinity Ventures and Shoedazzle founder Brian Lee.

Whisper is said to be valued in the $75 million to $100 million range.