Inevstors and traders are mostly active on twitter, if you don't have much fund for Ads placement on popular omega sites. Tweet, retweet and tagging of friends might do wonder and the cost is minimal as compared to placing Ads.
Paid advertisement is always better than the free advertisement. I don't think an exchange could be low on marketing funds. I think they should opt for paid advertisements which will give them far better results in quick time.
I guessed we already got the point here since the OP got their exchange to have an Estonian License with it I doubt that they are looking for free ways of promoting their website because if they will just rely on their friends and family to post tweets and retweets I doubt that it would have the same affect as promotions actually coming from ad pages. This kind of advertisement will only make them "scammy" looking as what people generally see on crypto related advertisements coming from people they know. Like what I said on my first post in this thread if they want to have the right audience its best for them to pick crypto ad networks to promote their banners for their site.