Twitter is set to secure a $1bn valuation from investors before it earns its first substantial revenues after the micro-blogging site raised $100m in new funding.

Insight Venture Partners, the New York venture capital firm, is leading a consortium of new and existing investors in the fast-growing communications network, according to a person close to Twitter. The website allows more than 30m members to post 140-character updates on the web or by mobile phone.