A Celebrity is using my federally registered trademark

Assuming that you have a valid trademark, you may be able proceed against the infringing party or parties. How this is done depends on the nature of the mark and on the nature of the infringement. You first have to decide if you want to try to resolve the matter through a cease and desist letter, negotiation or litigation (and if litigation, are you prepared for the potential costs in terms of time, energy and expense). Damages can include actual damages, statutory damages (damages that are awarded as a penalty and which are not tied to amounts lost by the owner or taken by the infringer) or the profits earned by the infringer. 15 U.S.C. §1117. There isn't much caselaw on hashtags yet, but it would be difficult to see how a hashtag could infringe on the deisgn elements of a mark, but certainly could infringe on the words that were registered. The important issue in any trademark case is whether the infringing use is likely to cause confusion as to the source of the goods. I can't express an opinion about that without knowing your mark or the infringing use, but suggest that you look at your mark and at the infringing mark and ask if a consumer would lliekly think that they were made by the same company. If yes, then you may want to look into legal action. Best wishes, Michael R. Morris