Shares of Google Inc. (GOOG) hit another all-time high Thursday, breaking through the $400 threshold, a move that may once again force Wall Street to rethink its price targets.

Google shares have been romping higher since it posted better-than-expected earnings last month and reported a "sea-change" shift by major companies to online marketing from print and broadcast.

While shares were up just less than 1 percent Thursday, the stock still pushed through $400, hitting a session high of $403.81. The stock added $3 to $401.15 on Nasdaq.

What's more, the stock is up nearly $100 a share, or more than 30 percent, since it reported earnings on Oct. 20 and prompted a number of Wall Street analysts to raise their price targets.

As of Thursday, six analysts had a price target of $400 for the company, according to Reuters Estimates. The highest mark is $450 a share, listed by both RBC Capital Markets and Lehman Brothers.

Shares of Yahoo Inc.(YHOO), Google's chief rival, also hit fresh five-years highs Thursday, as both companies benefited from optimism about online advertising. Shares were up 38 cents, or 1 percent, at $40.42 on Nasdaq.