There are several ways you can achieve this. Practically almost always looks better than something attempted in post. However, the roadrunner effect isn’t particularly realistic, so it’s often difficult to achieve without digital effects.
The first thing I would look into, if I were you, would be various particle effects. CC Particle World might be a good start. Some particle effects such as Trapcode’s Particular (my favorite AE particle effect) come with smoke/cloud-shaped particles, but in other cases, you’ll have to create one.
– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.