If my thesis is Social networking is a powerfull force in modern society. It helps us stay connected with friends, even if we don't show them the 'real' us and it has shaped current events and our views on these events...

will my topic be about facebook or myspace.

topic sentence 1: will be using a wall or commenting

topic sentence 2:social networking games?
topic 3:
topic 4:
I don't know what my topic sentence. hope I can get your feedbacks.

You're the one who chose this topic. If you cannot think of enough things to write about, choose a different topic.

However, I can't figure out why you are having any problem thinking of things to say. There are umpteen ideas here:
http://www.google.com/search?hl=en&source=hp&biw=1024&bih=413&q=social+networking+powerful+force+today%27s+world&aq=f&aqi=&aql=&oq=

And remember: Social networking includes much more than just Facebook. There's MySpace, Twitter, Photobucket, Craigslist, etc. Make sure you watch this and take notes:
http://www.youtube.com/watch?v=N2vARzvWxwY

Based on your thesis statement, it seems that your topic is about the overall impact of social networking on modern society rather than specifically focusing on a particular platform like Facebook or MySpace. Here's how you can structure your topic sentences for each paragraph:

Topic Sentence 1: The first paragraph can discuss the use of walls and commenting features on social networking platforms to stay connected with friends and the concept of portraying our curated selves instead of the "real" us.

To support this topic sentence, you could include examples of how people interact on social media platforms, the psychological effects of presenting a filtered version of ourselves, and the implications it has on our social relationships.

Topic Sentence 2: The second paragraph can explore the influence of social networking games on modern society.

To support this topic sentence, you could discuss the popularity and addictive nature of social networking games, their impact on mental health and productivity, and how they shape our perception of the online world.

Topic Sentence 3: The third paragraph can address how social networking has shaped current events and influenced our views on these events.

To support this topic sentence, you could discuss the role of social media in spreading news and information, the impact of viral content on public opinion, the rise of social movements through online platforms, and potential consequences such as misinformation or online echo chambers.

Topic Sentence 4: Finally, you can discuss the overall societal implications and potential future developments related to the power of social networking, tying together the previous points made in the essay.

Remember, these are just examples, and you can modify them to suit your specific arguments and evidence. The main idea is to maintain a logical flow and align your topic sentences with the different aspects of social networking's influence on modern society.