Although it sounds illogical, you might not recognize a hacked account at all. It works as usual, but could be abused in many ways for different activities.
Spam Posts and Links
Posting spam content is very common for hijacked accounts. In this case, your account is misused in order to post any kind of content. Your friends could take this content seriously and follow its message or click the link. It usually leads to some kind of scam website.
Likes and Shares
Your account could be used for liking and sharing defective content. This puts your friends at risk and this activity is done under your name.
Fake Promotions, Discounts or Giveaways
Sharing fake promotions, ridiculously great discounts or even free giveaways could cause your friends to put their credit card details somewhere and ultimately get scammed.