How google,youtube,facebook earn money?

[Deepak]

[D]

they run ads, and there are premium services that cost money. but it is mostly advertising

[Steve B]

1) Advertising

2) Products (e.g. Yahoo premium mail, Google App Engine, Facebook games, etc)

[thatguy52]

Sponsors.

[R@hul]

woah!! these guys totally make
bank. advertisement. here's
how it goes:
you get paid by people who
advertise on your site. if you
have, saaay 2,000 views on your
site, then they give you like
twenty bucks. the thing is, how
many people are on facebook
everyday, a ****-ton. ergo, how
much money they're making?
who knows. a lot.

[Ketan]

Advertisements are the basic funda.

The pages of companies are often liked and searched by people on facebook... this gives them another sales promotion advantage over their rivals.
Business and marketing firms also upload their videos and ads on youtube.

In this way google, facebook, youtube provide marketing support and get paid for such services.