Unfortunately, having an expired I-20 would make it impossible for you to apply for a tourist Schengen visa in the US. Local Schengen consulates ask for a valid I-20 in order to verify that you are a long-term resident. For example, here are the residency requirements of the French consulate in the US:
For non American citizens, a proof of resident status in the USA (green card, valid US visa and copy of valid I-20 or valid I-AP66, visas...). The visa AND the US resident status must be still valid at least 3 months after the last day of stay in the Schengen area (+ one copy of the visa, green card or relevant document). US pre-approval notices for US visas will be declined (only valid US visas affixed in your passport are accepted).
The Greek consulate has similar requirements:
For foreign students on F1 visas:
You can still transit through the Schengen area if your visa satisfies the conditions of visa-free transit.