Here is the very quick way to find your state senators: Senators of the 115th Congress. On that site, you can choose your state in the dropbox so you don’t have to scroll to search for your senators. Their office phone numbers and email addresses are provided. Calls are always preferable for activism undertaken for any reason, not just this one. If you’re hesitant to talk to a person in real time, you can always call after hours to leave a message. If you are still hesitant to do that (I get it, not everyone likes using the phone) but you still want to voice your opinion, then please send an email.
Again, the vote happens on March 12, 2018
EDIT: You can use the Resist.bot to send a text to your senators about FOSTA-SESTA if you don’t want to talk on the phone but you want something more immediate and direct than email.