No, They are quite different! Unfortunatley, for the first five years or so since I began playing guitar I would choose plectrums depending on their colour and not their thickness and texture. From time to time a student will show me a 'cool' plectrum with an interesting pattern or a photo of a boy band printed on them. Even worse still, those badly cut plectrums of old bank cards that are made from plectrum cutters! I always find the comical, cool and weird plectrums to have a generic thickness (usually too thin) and they have edges that are not designed to strike guitar strings.
After those years of using any old plectums that could be found from the back of the sofa, I have decided on which plectrums suite me, for whatever playing situation I may need them.
First of all, thicker plectrums make the guitar strings louder. Thinner plectrums sound much softer. Thicker plectrums can pick notes very accuratley, but when strummed can cause a harsh attack sound (like a sharp chugging sound) as I've found from recording acoustic guitars. Thin plectrums aren't very good for picking single strings as the plectrums are too flexible, on the other hand thinner plectrums are great from strumming acoustic guitars as you can strum the guitar hard and not really affect the attack (the first strike) of the strings.
It reallly depends on which sound you want to achieve. I never really knew the difference since I recorded myself playing. You should record yourself too.
For electric guitar, I exclusivley use 'Dunlop Derlin Standard plectrums (1.5mm Lavender)' as I feel I can get a good sound from the guitar strings and I can achieve a good dynamic range from strumming to picking.
When it comes to acoustic guitar I generally use 'Dunlop Nylon Standard (Grey 0.60mm)' as I can achieve a good balance between picking and strumming. If I was recording a strummed acoustic guitar I would use a thinner plectrum as I like the even sound they produce when strumming hard or soft.
Generally, try a few plectrums for yourself. Buy from a guitar store and not a toy shop. Try out different textures as some have more grip on them than others. They are not too expensive, so experiment with a defferent selection of plectrums to see what you like best.
A little tip... If your plectrums have a rough edge from playing them too much, strike the edge of the plectrum on a carpet (just like a match) and this will burn away the flakey plastic. Wow, a brand new plectrum!
I usually buy my plectrums from a strore, but if I can't buy them I get them from String Busters.