A tickle is an interpersonal activity done for the purpose of making someone laugh. It can be done in various ways, usually by having the person lightly stroke the other person's skin with a feather.
Empath: The Luckiest Smurf stories
Tickling in the EMPATH: The Luckiest Smurf story series is mostly done to Baby Smurf and the Smurflings by the adult Smurfs, although the adults can sometimes fall prey to being tickled, either as a prank or as a form of torture. Empath usually likes tickling in more intimate settings with Smurfette.
Second Smurfette Series
In "The Second Smurfette" series, tickling is usually done to Baby or Kate. But there is a forest called Tickle Forest. Tickle Forest has live vines that reach out to victims and tickle them until they cannot breath. The only way to stop the vines is to tickle them back.
Tickle Forest appears in the episode "The Place of No Return" where Hefty and Jokey became Tickle Forest's latest victims and had to be rescued by Lazy and Papa.
Hero: The Guardian Smurf stories
LD Stories/Expanded AU
Within The Light and Dark Series series, which crosses over with the Expanded Animated Universe, Jokey likes to tickle his fellow Smurfs when they least expect it; it is a more favorable act in comparison to his "surprise" boxes.
Brainy has admitted to being ticklish, so Moxette may tickle him when in his studio just to push his buttons. He is easily pestered by this, but has learned over time that she just wants a laugh out of him.