Social theory of Change and Youth Bulge theory both may work as your thesis framework indirectly. If it work then you can conduct content analysis.

Thank you Aqeela! I'll look into it.

not sure whether this fits in with your chosen methods. But how about thinking around social network analysis, which could then be related to various theories of social movement development/growth

http://www.nationalismproject.org/what/gellner2.htm

Hi why don't you reviews studies related to Nationalism... and from there you could derive some elements/ variables that might suit your context which will to be tested further. Example articles :

Rawwas, M. Y., Rajendran, K. N., & Wuehrer, G. A. (1996). The influence of worldmindedness and nationalism on consumer evaluation of domestic and foreign products. International Marketing Review, 13(2), 20-38.

Blank, T., & Schmidt, P. (2003). National identity in a united Germany: Nationalism or patriotism? An empirical test with representative data. Political Psychology, 24(2), 289-312.

Conversi, D. (1995). Reassessing current theories of nationalism: nationalism as boundary maintenance and creation. Nationalism and Ethnic Politics, 1(1), 73-85.

Rowe, D., McKay, J., & Miller, T. (1998). Come together: Sport, nationalism, and the media image. MediaSport, 119-133.

Depends highly on your specific research questions, I d say. In any case I expect that lit on nationalism is important for this kind of phd i.e. the role of the media in constructing/reproducing the nation i.e. Billig's banal nationalism, Anderson's Imagined communities etc. Sorry I cant advice on lit associating in particular social media and nationalism. But there should be recent publications on sth similar. Maybe search in journals such as 'new media and society'. 

I also recommend you to test two theories:

-1 / The theory of herd

-2 / Theory of power law

Even in a behavior consistent with nationalism, citizens can conduct on social media according to these two theories.

In line wiith Maria A., Anderson's imagined communities and Charles Taylor's Modern Social Imaginaries will lead you to a 'national imaginary'. However, in networked society this national imaginary would have turned to be a 'global imaginary'. See e.g.  Steger et. al. Justice Globalism.

May I have question about your thesis? What sort of social media do you want to study? is it just facebook and GooglePlus? are you focusing on Mobile apps such as instagram? Thanks.

I would suggest you to go through the "Theory of Network Society" by Manuel Castelles. I am also working on Social Media and Political Activism for my Phd research... I am considering this theory as my research framework.

Best wishes

@Mohsen Goudarzi, Facebook and Twitter to be exact. 

Social contagion and the crowd theory

You should have a look at Kubik's theory on mnemonic actors depending on what type of society you are covering. It's especially relevant for the post-soviet area.