Welcome to italki :-)

My First Time

Hi everybody!
This is my first time in these kind this type of sites.

I'm looking forward to your replies.

Bye!

My first time

Hi everybody!
This is my first time in these kind of sites.

I'm looking forward to your replies.

Bye!

You can say:

This is my first time in this kind of site

This is my first time on this type of site

This is my first time on one of these sites

You can say "first time in" or "first time on". I think "on" sounds more natural.