U2 stars Bono and The Edge have been named as individual investors in the storage website Dropbox, after the company posted a photo to Twitter of the rock stars with site founders Drew Houston and Arash Ferdowsi.

The U2 duo is set to make $1bn (£620m) from their investments in Facebook and have previously invested funds into Palm and Yelp under the Elevation Partners company of which Bono is co-founder.

"Dropbox is excited to welcome Bono and The Edge as investors. Thanks for the support and look forward to great thing!" the company posted on Twitter.

The cloud storage company - which recently announced that it refused an offer to be bought out by Apple - is just four years old but already has more than 50 million users and is expected to have generated $250 in revenue for 2011, according to Forbes.

This revenue figure is especially impressive, given that 96 percent of users opt for the free option, which gives them 2GB of free storage; the remaining four percent pay either $10 a month for 50GB or $20 for 100GB.

In an interview in November Houston told Forbes that sales would still double in 2012 even if no new customers at all signed up, because he expects current members to upgrade their price plan as the amount of storage they require increases.

The late Steve Jobs approached Dropbox in December 2009 with plans to buy the company - then just over a year old. Jobs proclaimed that it was "a feature, not a product" and, after talks with Houston, backed out of negotiations quietly, until knocking Dropbox at a Keynote in June 2011, where he claimed iCloud to be better.

Bono set up Elevation Partners in 2004 and invested $1.9bn into it. The U2 frontman then invested heavily into Facebook, injecting $270m into the social network between 2009 and 2010.

When the site floats on the stock market - expected to be in May, following the submission of its IPO in February - Elevation Partners will earn profits of around $1bn.

An investment of $100m into the consumer review website Yelp was also made by Bono and The Edge and, following Yelp's market cap of $1.4bn after floating in March, the U2 duo "tripled their investment" according to a source who spoke to the Guardian.