Thais' time spent online surpassed that of watching television, says Google Thailand.
The lead slide in a recent infographic tracking Thais online shows internet usage by teens and adults is past 50 per cent.
Thais spend around 16 hours a week on the internet, compared with 10 hours for TV.
But internet advertising spending remains very low compared with TV media, said Ariya Banomyong, the country head for the search engine firm.
Most Thais spent time on four online media: TV, computers, smartphones and tablets.
Based on a Nielsen study, Mr Ariya noted time spent on the internet via mobile phones accounted for 49% of all media use, edging out time spent watching TV at 36%.
"Advertisers need to focus more on online marketing and advertising to cash in on changing consumer behaviour," he said.
The Digital Advertising Association of Thailand (DAAT) said TV media still took up the majority of Thai ad budgets at 69%. Online ad revenue made up only 3% of total ad spending, while revenue from mobile ads was less than 1%.
All figures were from 2012.
However, the DAAT forecast Thailand's online media spending will grow by 50% to 4.5 billion baht this year thanks to increasing use of full commercial 3G.
The number of internet users in Thailand is expected to reach 42 million by 2016, up from 35 million currently.
Google Thailand found its search engine traffic on mobile phones surged from 10% to 40% of the total during the past 18 months, he added.
The top three internet ad buying sectors are technology and mobile firms, automotive and tourism operators.
Sitthichoke Nopchinabutr, director for telecom business of Thai Samsung Electronics, a top digital advertiser, said the company will double its digital media budget this year for both internet and mobile.
Samsung is also looking to spend more on emerging ad channels, including digital TV and satellite and cable TV.
Mr Sitthichoke said online media are an effective tool to help companies measure customer feedback and engagement.
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