Is there any way to find competitor advertisers who do advertise on Google or on sites who uses google ad services? I am trying to contact them directly.
Tools like spyfu can do it for you.
You will find the niche, the advertisers and their contacts too.
You can also check services like SERstat or SEO Power Suite.
SpyFu and SEO Power suite are the tools to find a competitor advertisers
There are some paid and free tools out there that shows you exactly how your advertisers advertise, how much they spend and so on:
SpyFu Keyword Research Tools
Searchmetrics
Similarweb.com
These are my first choices!