What type of forces pull plates toward each other?
plates are pushed together not pulled together.
At divergent boundaries new crustal material is formed. The new material is pushed outward in both directions from the mid ocean or rift valley where the new crustal material emerges from the mantel.
The size or circumference of the earth does not increase due to the creation of new crustal material. The outward push of the new crustal material eventually will meet the outward push of new crustal material being pushed in a different direction.
Where two crustal plates are pushed together it creates a convergent boundary. An example is where the pacific plate is being pushed under the North American plate. The North American plate is being created at the mid Atlantic ridge and pushed West. The Pacific plate is being created at Mid Pacific ridge and is pushed East.
They meet and the Pacific plate is subducted under the North American plate.