The combined value of venture-backed Web companies Facebook Inc., Groupon Inc., Twitter Inc. and others has risen 54 percent since June, Bloomberg reported.

As investors hurry to purchase stakes in privately held social media start-ups, the values of which are based on the prices institutions are bidding for privately held shares, that trend is expected to continue.

“You have an increasing number of wonderful companies that have already proven they have a lot of value,” said Eric Jackson, co-founder of CapLinkedInc, which helps connect private companies with investors online. “People naturally want a chance to invest in a company like that,” he said.

According to Nyppex LLC, which measured the value of 11 companies, Facebook’s worth jumped 56 percent to $41.2 billion as of Dec. 1 and Groupon’s value rose to $4.8 billion. Twitter’s value has more than doubled since June to $3.71 billion.

LinkedIn Corp., RockYou Inc., Linden Research Inc., Digg Inc., Loopt Inc. and Eventful Inc. are other companies tracked by Nyppex. The combined 54 percent increase of those companies’ values compares with a 21 percent jump in the Nasdaq composite index over the same five-month period.