News just in from my friends at Reuters:

NEW YORK, Jan 3 (Reuters) – Plaxo, an early social networking site that has been overtaken by Linked In and Facebook, is up for sale, The New York Times reported on Thursday in its online edition.

Quoting people briefed on the offering, the report said Plaxo was seeking as much as $100 million, and that it has hired Revolution Partners to handle the auction.

Plaxo has taken over $20 million in funding to date from backers including Sequoia Capital and DAG Ventures.

The company helps users synchronize address books and calendar data. When a phone number of someone’s contact changes it automatically updates in contact address books.

Plaxo said in mid-2007 that it had signed up more than 15 million users, although the number of currently active users is unknown. (Reporting by Ritsuko Ando)