BEIJING/NEW YORK: Google dominates global spending on digital ads while Facebook has the fastest growth among the major players, but both face a growing challenge from Alibaba and Baidu, the latest estimates from eMarketer have revealed.

Out of the $146bn expected to be spent on digital advertising in 2014, Chinese search giant Baidu and ecommerce firm Alibaba are forecast to be the third and fourth largest digital ad sellers in the world with market shares of 4.68% and 4.66% respectively.

While this is way behind the 31.1% share taken by Google, the two Chinese companies recorded the highest market share gains since last year apart from second-placed Facebook, which grew its global market share by two percentaqe points to 7.75%, and social network Twitter, which grew 71% year-on-year to take 0.84% overall share.

When combined with the 0.83% market share secured by Tencent and the 0.38% by Sina, the online media group, that means these four leading Chinese companies will account for 10.55% of all digital adspend this year.

Alibaba and Baidu's influence is even larger in the global mobile internet ad market, eMarketer said, where Alibaba is forecast to increase its market share from 1.6% in 2013 to 6.2% in 2014.

Meanwhile, Baidu will nearly double its mobile adspend share from 2.6% to 5.1%, although Google and Facebook are set to continue their leadership of the $40.2bn global mobile ad market.

Facebook is forecast to grow its share of mobile from 16.6% in 2013 to 18.4% this year while Google, at 40.5%, will remain by far the largest player despite seeing its market share drop sharply from nearly half (46.6%) in 2013.

Returning to the overall digital adspend projections, eMarketer also noted that Microsoft, Yahoo and AOL – three of the largest original digital ad sellers – have each lost market share.

Microsoft's global share fell from 2.84% in 2013 to 2.72% this year, Yahoo fell from 2.83% to 2.36%, while AOL's share decreased from 0.93% to 0.81%.

Data sourced from eMarketer; additional content by Warc staff