For the FBI specifically
Not explicitly. If you “open the door” to social media, such as saying you have 100 foreign Facebook friends or Linkedin connections, then they will probe further. They will ask questions pertaining to if you met these online friends, how you connected, their nationalities, and if they asked you any questions about your career. If you mention that you criticize the government on your social media, they will probe and see if you are plotting to overthrow the White House. If you mention you have a porn subscription, they will ask for details to make sure it isn’t illegal porn. Basically, don’t open any cans of worms and you will be fine.
The CIA will want ALL the info you have on your foreign social media friends. If you have 1,000 foreign online connections, you will be writing up 1,000 foreign contact documents.
Now even if they don’t ask about your social media during the polygraph, the agencies are still allowed to look at whatever you have that is public only (private pages are safe from this). See SEAD 5 Section E.