Popular microblogging and social networking site Pownce will close forever on 15 December, after it was acquired by rival Six Apart, the company behind Movable Type, Vox and TypePad.

Pownce users have the option of exporting their messages in a format that can be uploaded to Vox, TypePad or Wordpress, at http://www.pownce.com/settings/export.

There’s no word yet from Pownce about the status of Pro accounts, which gave users access to extra features and cost $US20 per year. Six Apart has offered Pownce Pro users a free TypePad account for a year.

“We’re bittersweet about shutting down the service but we believe we’ll come back with something much better in 2009. We love the Pownce community and we will miss you all,” said Pownce co-founder Leah Culver in a blog post.

Chris Alden, CEO and chairman of Six Apart, said that Pownce and Six Apart shared a ‘common vision’ about making the internet more social.

“We have been impressed not only with the vision for Pownce but the great work of Leah Culver and Mike Malone and are very happy that they will be joining us. We’re also very excited to welcome Kevin Rose and Daniel Burka as advisers to Six Apart,” said Alden.

“The Pownce team and Six Apart share the same passion for social blogging and we’re really proud to have them on board.”

Culver agreed that the merger was a logical choice.

“We’re very happy that Six Apart wants to invest in growing the vision that we the founders of Pownce believe so strongly in and we’re very excited to take our vision to all of Six Apart’s products,” she said.

“We’re looking forward to being a part of the talented group that has created amazing tools for blogging and publishing.”