If you have the time and resources, a combined marketing and sales approach would really deliver. Ideally - these people and/or teams work together (which drives much higher results).

Sales - Cold emails do work. My advice would be to keep copy short since people don't always read cold emails and they certainly won't read long ones. Develop a clear sales funnel as well and create marketing content along the way to push people down the funnel.

Marketing - Marketers help bring in marketing qualified leads (MQLs) that sit at the top of the funnel. It's sales' job to push these leads down. Marketing techniques that I think would work would be social (LinkedIn is your best bet here), content such as blogging (get something for Google to read to rank you), and even email if you have a list or want to start developing one. The best rule of thumb for a marketing campaign is to provide the potential leads VALUE. Don't start with the hard sell, give them content they can use, find trustworthy, and want to share.

Happy to chat more!