YouTube has been one of the most popular websites on the Internet since it launched. The site allows people to upload their own video content, listen to music and watch anything from tutorials to sports. YouTube was founded by three PayPal employees Chad Hurley, Steve Chen and Jawed Karim in February 2005. The popular website was bought by Google within a year since it launched.
Youtube’s logo is split into two parts, where both words “ You,” and “Tube” are typed in a Bold Helvetica typeface. “You,” is written in black and the word “Tube,” is inside a rounded red rectangle in white. “Broadcast Yourself,” which is the site’s slogan also sits right underneath the company’s logo. YouTube kept this logo from 2005 up until 2011.

(Photo from 2005-2011)

The first modification of YouTube’s logo was in July 2011, which was a part of the Cosmic Panda (a trial design for the website) experiment. Followed by that experiment, YouTube made the modified design its official logo months later. This time the rounded red rectangle became a deeper shade of red and the site’s slogan no longer sat underneath the logo. YouTube continued this logo from 2011 to 2013.

(Photo from 2011-2013)
As of December 19, 2013, the rounded rectangle was reverted back into a lighter shade of red. The word “You” is a deeper shade of black and the shadow was removed from behind the word “Tube.” This logo has been used since 2013 up until last year.
Today all gradients have been removed from the logo. However, YouTube’s logo app designs have changed numerous times. The first one app design was of a old television, whereas the second design has the words “You” on top of the word “ Tube,” which are both in a white box. The site’s latest design is of a red and white play button that sits in red square.

(Photo)
References
http://logos.wikia.com/wiki/YouTube
http://www.famouslogos.us/youtube-logo/