SAN FRANCISCO — Twitter was valued at almost $10bn by one of its investors, about 10% more than a previous estimate, indicating that shares are appreciating ahead of a possible initial public offering (IPO) for the microblogging service.

GSV Capital Corporation owns 1.9-million shares of Twitter valued at $35.2m, or about $18.50 a share, it said in a filing last Wednesday. Based on a fully diluted share count of almost 530-million, that makes the firm worth about $9.8bn.

Twitter is becoming more valuable as the San Francisco-based social website boosts revenue from advertising and moves closer to a predicted IPO. In January, it was valued at about $9bn when a fund managed by BlackRock bought stock from employees, up from the $8bn valuation in a 2011 investment round led by DST Global, people with knowledge of the matter have said.

GSV CEO Michael Moe declined to comment. Twitter did not respond to a request for comment.

GSV, based in Woodside, California, is a publicly traded investment fund that primarily buys shares of closely held technology companies on the secondary markets. The firm first sold shares to the public in April 2011.

The fund reported total assets of $245.4m at the end of March, and Twitter is the biggest holding, accounting for 14% of assets, including $34m of common stock and $1.2m of preferred shares. The next biggest holdings are Palantir Technologies, Dropbox and Chegg.

Twitter, founded in 2006, is offering new forms of advertisement and expanding to international markets in its bid to reach $1bn in revenue next year.

While CEO Dick Costolo has said management is not concentrating on an IPO, Twitter is widely predicted to hold a share sale soon to help it bankroll expansion, and give early investors a way to realise financial gains on their holdings.