These are the builds I use in Arena when I play Thor. He already passively has an increased movement speed. His hammer hurts so you want to have attack speed, but you end up doing most of your damage with abilities. With the movement speed and attack speed he is unstoppable, just add a "little" physical power and he is a true God. His ultimate is great for ganking foes who have broke away from the battle with low health that are running to base. Also, Thor's ultimate can act as a gateway out of a gank or a team up, allowing you to fly into your base untouchable.
Abilities: I use Creeping curse because it slows the enemy immensely and helps a ton when you run so fast. I also like to use Girdle of Might because it's an big power buff when you really need it since you possess a lot of physical power.
Consumables: I recommend buying Health AND Mana potions at start for camps. Not having Meditation thirsts you of mana early on. Your thirst for mana diminishes later in the game. When you have bought everything and have upgraded your abilities, buy a Potion of Physical Might to give you an edge.
Buffs: The red hulahoop(DMG)is very helpful early on, like I said before if you don't want a bunch of HP/Mana Potions then buy Potion of Physical Might to stack with your damage camp buff at the start. However, if someone steals your DMG buff then attack speed will be fine.
Feel free to blend the builds to your liking. Remember every game is different and you may find the need of more tankier items. Always build according to the game.
Thor is quick, he is strong, and he can be very evasive is played correctly. He is a great ganker and provides VERY high single target damage but also some AoE damage as well.
Thor's #1 ability, when casted the second time, Thor will teleport to the location of the hammer. This makes it easy to disengage from crowd fights and to get back to base where you can replenish health, mana, and purchase much needed items. However, if you choose not to teleport to the hammer, it will act as a boomerang and cause damage to the enemy going and coming. Thor's #1 ability is best when used after stunning the enemy with Thor's #2 ability. Just line up the shot and let the hammer hit the enemy two times. On occasion, it will be necessary to teleport to the hammer and finish off the enemy with Thor's #3 ability.
Hits VERY HARD
LOTS of Single Target Damage
Quick on his feet
Squishy at the beginning
Goes OOM very easily in the beginning