Teleporter 2: Sea level island: Go to the beach closest to the teleporter (not back to the beginning). The seed is on top of largest of the group of floating asteroids.
Teleporter 3: Star plant roots: On the opposite side of the star plant branch. The seed is on the next island with two cacti, on top of one of them.
Teleporter 4: Big Mushroom Island: Can't remember exactly but it was close nearby, just walk around the area... I think it was beyond the arch on the backside island wall...
Teleporter 5: Small Mushroom Islands: Downwards from this position, there are two islands connected with a path of floating pebbles. The seed is that path.
Teleporter 6 (1): Big Forest Island: There are two canyons directly below the teleporter. The seed is at the end of one of those canyons, on top of some pebbles.
Teleporter 6 (2): Big Forest Island: Upstream the river, between the forest and the river is a large group of spikey bushes. The seed is inside there.
Teleporter 7: Small Snow Covered Islands: If I remember right, this one is just further down on the island directly below, on a venus fly trap plant. If not there, it must be another island nearby on a venus fly trap.
Teleporter 8: Asteroid Field: Look downwards, the seed is very close on an asteroid next over.

by:Klaimen

and video by Tenik