Yes, you need Line of Sight.

One other difference from movement is that you can teleport while immobilized, restrained, or grabbed.

From the PHB3 section on Teleportation:

• Destination Space: The destination of the teleportation must be an unoccupied space that the target can occupy without squeezing. If arriving in the destination space would cause the target to fall or if that space is hindering terrain, the target can make a saving throw. On a save, the teleportation is negated.

Yes, you need Line of Sight.

One other difference from movement is that you can teleport while immobilized, restrained, or grabbed.

From the PHB3 definition of teleportation

• Destination Space: The destination of the teleportation must be an unoccupied space that the target can occupy without squeezing. If arriving in the destination space would cause the target to fall or if that space is hindering terrain, the target can make a saving throw. On a save, the teleportation is negated.
• Line of Sight: You must have line of Sight to the destination space.
• No line of Effect: Neither you nor the target needs line of effect to the destination space.

Yes, you need Line of Sight.

One other difference from movement is that you can teleport while immobilized, restrained, or grabbed.

From the PHB3

TELEPORTATION You use these rules when you use a teleportation power on a target. which might be yourself. another creature, or an object.

• Instantaneous: Teleportation is instantaneous. The target disappears and immediately appears in the destination space you choose. The movement is unhindered by intervening creatures, objects, or terrain.
• Destination Space: The destination of the teleportation must be an unoccupied space that the target can occupy without squeezing. If arriving in the destination space would cause the target to fall or if that space is hindering terrain, the target can make a saving throw. On a save, the teleportation is negated.
• Line of Sight: You must have line of Sight to the destination space.
• No line of Effect: Neither you nor the target needs line of effect to the destination space.
• No Opportunity Actions: The target doesn't provoke opportunity actions for leaving its starting position.
• Immobilized or Restrained: Being immobilized or restrained doesn't prevent a target from teleporting. If a target teleports away from a physical restraint. a monster's grasp, or some other immobilizing effect that is located in a specific space. the target is no longer immobilized or restrained. Otherwise,the target teleports but is still immobilized or restrained when it reaches the destination space.

Yes, you need Line of Sight.

One other difference from movement is that you can teleport while immobilized, restrained, or grabbed.

From the PHB3 section on Teleportation:

• Destination Space: The destination of the teleportation must be an unoccupied space that the target can occupy without squeezing. If arriving in the destination space would cause the target to fall or if that space is hindering terrain, the target can make a saving throw. On a save, the teleportation is negated.