Some great suggestions by Adomas. Here are few more you can try -

- target people who like brands (which you sell on your site)
- target people who like 5-10 competitor's sites (for each product category)
- find pages/interests liked by people who like your page and get ideas from there
- expand your lookalike audience beyond top 1%

Above should help you expand your reach. Now to increase conversions, you must do re-targeting for those who visit the site and you must keep expanding the lookalike audience based on your "buyers" list.

If you need more help in setting up or scaling up huge campaigns, let me know.