Fantastic topic. As you know over the past two decades, there has been an increasing focus on the development of Information and Communication Technologies (ICTs), as well as the impact that they have had on the tourism industry and on travelers’ behaviors particularly using social media!
However, research on what drives consumers to purchase travel online has typically been fragmented. In order to better understand consumers’ behavior toward online travel purchasing, a recent research study (Amaro, and Paulo, 2013) offers a review of articles that were published in leading tourism and hospitality journals, the ENTER proceedings, and several articles from other peer-reviewed journals, found on the main academic search databases.
The antecedents of online travel shopping found are classified into three main categories: Consumer Characteristics, Perceived Channel Characteristics, and Website and Product Characteristics. Finally, in this study the authors identified several gaps and provides some orientation for future research!
Amaro, Suzanne, and Paulo Duarte. 2013. "Online travel purchasing: A literature review." Journal Of Travel & Tourism Marketing 30, no. 8: 755-785.
In terms of methodology, what I can think of is a two-stage research. In the first stage, you may conduct a content analysis of social media promotions. In the second stage, you may develop experimental stimuli derived from the content analysis and conduct experiment to test the impact of social media promotions on customers' purchase of air travel services.