How can I transfer online stats between Xbox Live accounts?

I have recently decided to create a new Xbox account, but all of my online data is stuck on my old account.

I know how to transfer offline data like single player using horizon but I do not know if there is a way to transfer online data (e.g CoD Guns and stats used in multiplayer)

It would be great if someone could help me out!

There is no way to transfer "online" data like that.

Horizon works by modifying the User ID embedded in the CON package, and re-signing the package to make the console accept it. When the console scans the packages, it will see these packages under the new user, and thus the transfer works.

Online services, such as Call of Duty, use a different method. Specifically, Black Ops, worked in a way where a small file was downloaded to the system and loaded in memory. This small file contains all of the user data, and gets uploaded back to the server after the end of a match. My answer is specific to Black Ops because it is how I modified my online stats on the Xbox 360. I am not aware of how future iterations of CoD do it, but it is likely similar.

Other games such as Halo 3/Reach will keep the data on the game servers at all time, and simply synchronizing the stats to the local console as necessary.

In any case, it is not possible to do the transfer generically. A method would have to be developed for each game, and even then those methods can be patched or blocked. Even then, not all games would do it in such a way that it could be modified in the first place.

Therefore just stick with transferring the offline content.