Facebook IPO price range's midpoint $31.50:

SAN FRANCISCO (Reuters) - Facebook Inc plans to price its initial public offering at a range with a mid-point of $31.50 a share, a source familiar with the IPO told Reuters on Thursday.

The source, who declined to be identified because the information has not been publicized, did not elaborate on other details.

The world's largest social network is expected to raise as much as $10 billion this month in what would be Silicon Valley's largest-ever market debut. The company had been expected to release an updated IPO prospectus this week.

(Editing by Gerald E. McCormick)