These charts show how far Google and Facebook are ahead of Twitter

Facebook announced in Thursday it had reached the important milestone of bringing on board 2 million active advertisers. That's a 33% increase from the amount it reported in July 2014, and is up 100% on June 2013.

That number doesn't only highlight Facebook's direct revenue opportunities: It shows - if anyone was still making direct comparisons between the two businesses - just how far Twitter has to travel in order to catch up. And it also indicates how quickly Facebook is gaining ground on Google, which has been in the advertising business far longer.

A note from analysts at Macquarie Research estimates that only Google has more direct advertising relationships in the digital advertising space.

Macquarie estimates that Google has approximately 4 million advertisers (the company does not disclose its international advertiser numbers, so it could be even more than that.)

Meanwhile, Twitter announced at its analyst day in November it had 60,000 advertisers, although Macquarie note that number is probably growing quickly.

This chart shows Facebook's rapid growth in obtaining advertisers since Q2 2012. Google's numbers are estimated, based on the number of advertisers in the US adjusted by the relative share of US vs. international revenue for each year. The chart also shows the impact of Google's 2012 cleanup of "bad actors" who were using its network for "harmful or deceptive purposes."

Facebook still has room to grow the average spending per advertiser, which has only risen modestly over the past three years, according to Macquarie's estimates. Macquarie believes Google's growth per advertiser spend is likely driven by YouTube and display growth, as well as its ongoing purge of low quality advertisers.

Macquarie chose not to make a comparison with Twitter here because its strategy has largely focused on big brand advertisers, only recently looking to small-to-medium businesses.

That means its $21,000 earned per advertiser in 2014 is more than $5,000 higher than Google and nearly three times Facebook's total.

Macquarie says Facebook's 2 million advertiser number is significant because it shows the power the social network has to drive a network business, which could even extend to search advertising. Having so many advertiser relationships means Facebook has the power to more effectively monetize third-party content and place ads from its system on sites other than its own (that's the idea of the Facebook Audience Network and its Atlas ad server.)

Macquarie explains how that could extend to search, which it says could equal a "nightmare scenario for Google" were Facebook to focus its efforts there.

Importantly, over time, these ads can also be used for search, both on FB and off. This does NOT mean that FB has to convince users to begin searching for widgets on FB and using FB to replace Google. FB can use its scale of advertisers to drive the sponsored results for other search players.

For example, say YHOO wants to monetize its mobile search with non-MSFT ads (the Bing deal is not exclusive for mobile). A user searches for "widget" on YHOO mobile search. YHOO could use Bing to power the organic search results and then use FB to display sponsored results. Or a user searches for "widget" on an AAPL device. AAPL could use third-parties (Wikipedia, Bing, AMZN, YELP, etc...) to drive the organic results and then use FB and some combination of all those third parties to also drive sponsored links. Sophisticated algorithms could determine which to prioritize on a search-by-search basis.

This would take time, but is feasible. Facebook's meteoric growth is showing no sign of let-up.