Auto Trader's operating profits rose by 9% to £109.6m in the six months to the end of September and pre-tax profits increased 10% to £105.4m.
Revenues were 7% higher at £165.0m and cash generated from operations rose 11% to £114.2m.
The group declared an interim dividend of 1.9p per share - up from 1.7p last time.
Chief executive Trevor Mather said: 'We have delivered good growth in the first half, as we continue to create a more efficient marketplace for car buyers, manufacturers and retailers.
'Our business has continued to perform strongly, underpinned by the successful launch of our retailer advertising packages in April.
'The new packages provide additional products for all customers and offer new opportunities for retailers looking to compete more effectively on the marketplace.
'The results highlight the resilience of our business considering the slowdown in new car transactions and a flat used car market.
'We will continue to benefit from the increased focus retailers are putting on the larger opportunity they see in used cars, where we are the clear market leader.
'We remain focused on improving the car buying and selling experience for consumers, who can now benefit from our free valuations and finance tools, thousands of dealer and car reviews, and will soon be able to search for their next car based on monthly finance payments.
'The Board is confident of delivering its growth expectations for the remainder of the year.'