It all depends on your audience. You can create interesting articles and post links on forums. You can also create a Facebook page and post there, but be aware of financial services promotion restrictions, so you will have only organic visitors. Twitter is also interesting platform for promotion, as you can test different hashtags.
Best to read the Forum Rules. Normally the best place is in your signature once you become an established member. Make sure to read all the rules or you will pegged as a spammer and banned.
You can run your ads in the business section. I believe DP allows you to choose which section of the forum to run ads, I think that is what you are asking. Business forum... https://forums.digitalpoint.com/forums/general-business.33/ eta: OOPS, old thread, sorry.