Hi,
If you want a contact me button, you can just activate the "Display a contact button on the product page" setting of the HikaShop configuration.
Note however that this option is only available in HikaShop Essential and Business.
Also, this will send an email with the message of the user.
If you need to have different receivers for different products because they are sold by different persons, the best is to use HikaMarket Multivendor:
www.hikashop.com/hikamarket-multi-vendor.html
With it, you can link each product to its corresponding vendor, and the vendor will be notified of the contact request instead of you.
To allow you to enter extra information for each product, like a FB messenger link, an email address to contact, you need to create custom fields of the table "product" via the menu Display>Custom fields. This is also only available with HikaShop Essential or Business.