target audience being SME's, Startups, Entrepreneurs
I would start by selecting the most popular categories/fields that the users are looking for freelancers (based on Google Adwords Keyword Tool or maybe checking Fiverr - if their services are the similar to the ones you plan to offer).
Then, to intensive, but focused/targeting marketing* for freelancers and users of the field that you chose.
Repeat the above process for the top 5 categories and then either repeat or move on to the next categories.
As for the actual marketing platforms/methods, this really depends on the categories of services/the type of freelancers, your budget etc.
I've successfully helped over 300 entrepreneurs, and would be happy to help you. The first (15min) call would be free so that I can get the information. You can use this link to schedule: https://clarity.fm/assafben-david/free-advice
Well done for creating a startup! Try enjoy the ride...