It's never a bad idea to reach out to your social media fanpages to gain subscribers. When you do, just be sure to include the language necessary to make this a compliant opt-in.
Whether you just add the "Text KEYWORD to 29071" in your posting text or create an exciting graphic inviting your followers to subscribe, you want to include the opt-in language to stay within TCPA regulations.
"By texting this number, I agree to receive recurring automated text messages at the phone number provided. Consent is not a condition to purchase. Msg & data rates may apply. View our Terms of Service for details."
This should cover the bases for your shop!
Please let us know in chat if you have any additional questions!