The purpose of this thesis is to analyse and to explore how B2C e-commerce businesses could use social media marketing strategies to increase their consumers purchase intentions on their sites. Findings enabled the development and research of a comprehensive social media marketing system which includes a general set of components and tools aiming at increasing purchase intentions on such sites. The theoretical framework of the thesis is based on literature as well as previous studies of Social Media, Social Media Marketing, Social Media Marketing System, E-commerce, B2C, Social Commerce, S-commerce, Online Purchase Intentions, Trust and Social Trust. A conceptual framework was created and led the research method which used a convergent parallel mixed method design that includes gathering and analysing both qualitative and quantitative data. The data is gathered from potential users and clients of the system and led by the user-centered design (UCD) process. The obtained qualitative and quantitative data was analysed separately and then merged together by a side-by-side comparison. With the use of this approach, several ways businesses can increase consumers purchase intentions towards their B2C e-commerce site were discovered. Social media presence, published content, publishing frequency, content type, special sale promotions and social media friends are variables that have been found to be influential upon purchase intentions. The integration of a social media marketing system combined with these variables was found to be a successful tool for B2C e-commerce businesses wanting to increase consumers purchase intention through social media networks.