Have you put in a report? It might not be a lot, but at least the police department will be aware and be able to start an investigation.

If there's any anomalies that you can recall in the least in the time span where you remember having her and not will help. Also the location you were at. If you have anything that has her scent, you can probably have a Pokemon that can track use it and try to find her trail. Scent can be a very handy thing, especially if your Lilligant has a strong scent to identify it.