Roblox Cframe lookVector Isn't Moving Part?

The way to fix this is quite simple.

Like Ahmad said, moveTo is used for models that doesn't have a primary part. But it is not only that.

One thing that Ahmad forgot is that 'lookVector' is not a CFrame, it is a Vector3 instead.

In this fragment, you did

moveTo(player.Torso.Position + player.Torso.CFrame.lookVector * -5)

That would be fine, if you didn't use a numerical value with Vector3's. To fix this, instead, your code should be

local player = script.Parent
local jetpack = game.ReplicatedStorage.Jetpack;
local jetpackClone = jetpack:Clone();
jetpackClone.PrimaryPart = jetpackClone.Core;
jetpackClone.Parent = player; -- Is the 'Player' a Player, or a character??

local weld = Instance.new("Weld", player.Torso) -- We use 'Weld' here, instead of Motor6D
weld.Part1 = jetpackClone.Core;
weld.Part0 = player.Torso;
weld.C0 = CFrame.new(0, 0, -5); -- We use the C0 property of Weld's

That should do it for welding the jetpack to your torso. Though, I would check if the CFrame is correct in it, I am not sure if it is or not, but if the jetpack appears in front of your torso, then replace weld.C0 = CFrame.new(0, 0, -5) to weld.C0 = CFrame.new(0, 0, 5).

Hope my answer helps!

moveTo is used for models that doesn't have a primary part. Which can be inaccurate. Instead use :SetPrimaryPartCFrame() also u were adding Position+CFrame(it would cause an error did u check output?)