There are webmaster forums out there, such as this Internet Marketing community, and others such as WebmasterWorld, etc., but the days of spamming on forums and gaining backlinks or traffic are loooooong gone.
How you are planning to increase your traffic by posting on forums? If you are just going to signup and post about your website there, it would be spam. Forums are for helping each other as community, not to get traffic.
If you are looking to increase your traffic, use white hat techniques
You can do the following
Hire people who would build backlinks for you, as well as remove toxic backlinks. It will help your ranking as well as traffic.
Advertise on Google using adwords
Write content that is sharable and share it on social media. You can again hire people to do graphic design for social media or write content.
There are many forums like upwork, freelancer, elance where you can find talent.
You can also try micro-job websites like fiverr or yooker dot com. Yooker is growing community of seo freelancers who offer their services from $4 to $100. These freelancers are ranked at various levels according to customer reviews that enable you to select best for your requirements.
Hope this would help you.