I am Menelaos and I create Writer's PlayBook. Planning to create a campaign related with my soon to be launched screenplay book, I have concluded at about 2 sites from ProBoards as possible, who knows, affiliates, another forum I like a lot, Mythic Scribes, maybe and thinking of what should I do with networking to come up with activity. My forum already has content in it, but content written in English language, I write in both Greek and English is not much. This is the case.
Baring in mind advertising with ProBoards I see a CPM of, huh, 1 dollar, that is per thousand impressions, meaning ad exposure but not clicks. A cost of e.g. 30 dollars per 2 months seems reasonable. My question is, is getting 30000 impressions per 2 months from your experience effective in terms of scaling up actions and what should be the prerequisite creative volume to make it effective? Would it be effective for a forum of 3 members for now, where as is, only 1 has created a discussion reply?
I'm going to give you an opinion based on experience with different types of marketing. I do professional social media marketing for my employer's WordPress site. Her website will receive thousands of impressions, but since we offer a very specific type of business, only very specific people will click the link to visit her page. However, one client will end up providing her with at least $8,000 in business. So, in this instance, advertising is constructive.
I advertised my forum once on Proboards where a banner of my choice appeared on other Proboards forums. So, the targeted audience was obviously people who liked forums. My forum also once had the privilege of being a featured forum at one time right on the bottom of Proboards.com. I did receive a TON of clicks actually and had hundreds of guests per day. However, out of those thousands of guests, only a few people joined, and out of those few, only a handful became permanent and active members.
I don't think paid advertising is currently right for you. You may receive impressions and even clicks, but if your site is not currently active, it might not be appealing to your target audience. I would spend some time building up activity on your forum before you spend any money promoting it to others. My opinion is that your forum doesn't completely look ready to be marketed. I would encourage you to build up some more activity and make it more enticing to your target audience. Unless you have very specific deadlines, you don't have to rush this process.
Keep in mind that this is just an opinion and you are free to disagree.