Once someone very clever said: ´The most amazing thing Satan did was making people believe he doesn´t exist at all.´

This is the situation today.
Most people dont´ believe God exists and for them - consequently Satan doesn´t exist, too.

What makes a difference whether one believes both God and Satan exist? The difference is that God and Satan have different plans with us.
The devil´s plan is to mislead as many people as possible into sin.

If you ask people on the street to tell how they might imagine satan - most of them would think of a creature like the figure below:
 

Despite the fact that he would be very “head-heavy” - this imagination is absolutely wrong. Jokes aside.
Satan, or Luzifer once was the most powerful and most b e a u t i f u l angel God created. He and some other angeles rebelled against God and they had been cast out of Heaven (heading earth).
But the creature shown above is only useful scaring children and horror movie addicts.
You can´t see Satan at all! He is a spiritual being. He always shows up in disguise. Yes, Devil in disguise. Just like in paradise where Satan talked to Eve as a snake and seduced her to eat the forbidden fruit.
The only time Satan showed up without a mask was when he tried to tempt Jesus. Satan offered Jesus all kingdoms of the world if he would worship him.
This story means nothing more and nothing less that Satan is the ruler of this world.
“But GOD created this world”, you will argue. Yes, He created the universe and this planet and all what lives upon it. But God created all things perfectly until sin polluted His creation.
This sin was Adam´s and Eve´s disobedience on one hand and Satan´s rebellion against God almighty on the other.

May be you know the tv show ´C. S. I.´ - I once was a fan as well. In every case they investigate the crime scene very carefully and by extraordenary methods they always find out who´s to blame.
So if you investigate all bad things here on earth - you will always find evidence pointing to Satan.