Example: Me i want to join to my friend using the TeleportService, when i typed his name to the bar and pressed enter my character will be teleport to my friend.
If you are talking about teleporting them to another actual place where the friend is, I am not sure if this is possible. But if you mean just teleporting the character to some coordinates in the same place then you do not use TeleportService at all.
In order to get a list of a players friends, I believe you might need to use a WebAPI, so you’ll need to use HTTPService, and a you might need to use a web proxy since roblox.com links don’t work IIRC
I’m on mobile at the moment so I can’t write anything major currently, however there should be an example of how to use those two functions on the pages, then you might be able to find where to get the specific web api(s) for a players friends list elsewhere. I will try and update this post if i can find it myself.