Worldwide, probably a few thousand: http://en.wikipedia.org/wiki/Asatru#Demographics
many people think he was very Christian but this is not true, the only religious believe he had was Norse mythology or maybe atheist
The vikings didn't believe in just one God, they believed in many, which is called polytheism. They believed in the Norse gods such as Odin, Thor, Loki, Frey, etc.
Only a very small percentage of the worlds population know what the Norse myths are about.
It's all in a matter of opinion. I personally love Norse Mythology because I myself am Norse. It is not a very popular mythology and not many people know about it. Many people don't like it because of it's dark depressiveness and terrible endings. But there are some good stories in it.
There were 9 Worlds in Norse MythologyAsgardVanaheimAlfheimMidgardJotunheimSvarltalfheimNidavellirNifleheimMuspelheim
There are many Norse gods. Odin, Thor, Loki, Freya, Frey, and Ullr are some.
An Introduction to Old Norse has 412 pages.
Thor was/is famous for many things, most people know him for being the Norse God of Thunder.
Norse influence on English is profound. The Norse people founded many important British cities, such as Dublin and York, and a large part of Britain, called the Danelaw, was under Norse control for centuries. The pronoun "they" is Norse ( the Old English word for they was the same as the word for she). All the sk- words like skiff and skirt, having English cognates in sh- ( ship and shirt ) are Norse. Also the loss of declensional endings in English is attributed in part to Norse influence.
Frigg, sometimes anglicized to Frigga, was the wife of the god Odin in Norse Paganism. People of the Asa-religion (Norse mythology) lived in the time of vikings, around 1000 AD. This means the people who worshipped Frigga (and many other gods) were the vikings.
There are 9 worlds in Norse Mythology, not counting the Tree of Life. In Norse Paganism 9 and 3 are sacred numbers.