Keyword searches are normally available through the individual microblogs, however Twingly combines the results through the various websites in a single interface.
The new service also generates RSS and email alerts on keywords, usernames or tags mentioned in microblogs.
Pownce went offline in December 2008, but the archive of posts remains searchable.
Martin Kallstrom, Twingly CEO, said: "Until now the tools available have only been able to search one microblog service at a time, which has made this growing arena of the internet hard to penetrate for new users.
"At the same time, we have seen how this kind of service is becoming increasingly important.
"The latest example was the direct reporting from the Mumbai terrorist attacks in November when Twitter became an important news source, or during the presidential elections in the US where Barack Obama gained over 100 000 supporters in the same service."