The newspaper group will pay an initial £9.2m to purchase Find a Property and pay outstanding loans. Further payments will be made depending on the website's performance up to 2007.
Find a Property, the third most visited property website in the UK, will be run as a standalone operation. It is currently profitable and generates revenues of £2m.
Andy Hart, managing director of Associated New Ventures, said: "Property is a key market for our newspaper titles and we want to increase our presence in the digital sector. Find a Property is a perfect fit."
The online property market is worth an estimated £20m a year in advertising revenue, with this expected to rise to £80m by 2008.
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