The changes follow the launch of a new server system which Yahoo said makes delicious.com quicker and more reliable.
A company statement said: "Since we've grown from 300,000 to five million users since being acquired by Yahoo! two and a half years ago, a new platform was in order.
"It's now faster and more reliable, and will enable us to keep up with our rapid growth."
The new search feature enables users to search within one of their tags, another user's public bookmarks, or their own social network.
In addition, Yahoo has updated the del.icio.us user interface to improve usability and add new features, such as selectable detail levels and alphabetical sorting of bookmarks.
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