tikli

One root, no seam. Tikl- is indivisible, and the temptation to find a tik- plus something is worth naming because Esperanto trains you to look for exactly that. There is no -li suffix in the language. The endings that follow a root are -i, -o, -a and -e and nothing else, so any l you see before them belongs to the root or to a real suffix like -il-, and here it is the root.

The derivations are all useful. Tiklo is a tickle, tiklema describes somebody who is ticklish - literally inclined to be tickled - and tikleti is the light version, the feather rather than the fingers. The one to watch is tikla, which has gone metaphorical exactly as English delicate has: a tikla demando is a ticklish question, one you handle carefully, and it has nothing to do with laughing.

The sensation and the act are the same verb. Esperanto does not split tickle-because-I-am-doing-it from tickle-because-something-itches, so la lano tiklas is as good as li tiklas min. If what you want is a persistent itch rather than a passing tickle, the word is juki, and that one is not funny.