I talked about "Pelasgians" in a thread with is roughly parallel to what you are asking here over here. But in short: there is no such thing. It is a catch-all term which is increasingly useless as we learn more about the pre-Indo-European Aegean. Go to that thread for a good reference book on the topic.

edit: see also here

The Greeks of the Classical period had no knowledge of the past beyond what they made up about the stuff that they saw that was clearly older than they were (e.g. the Mycenaean walls of the Athenian acropolis). They invented a mythical past for themselves. Among these inventions were the "Pelasgians".

Replies of mine that are relevant to your question can be found in these threads:

• The Pelasgians are frequently mentioned in Classical and Hellenistic Greek literature as a non-Greek people who lived in Greece in the far past. How likely is it that these references are distorted memories of the Mycenaean era Greeks ?
• What was the relation between the mycenaean(17th-12nd century BC) and the ancient(8th-2nd century BC) greeks?
• Are most Ancient Greek myths “set” in Mycenaean Greece? (An especially useful book for you is John Boardman's The Archaeology of Nostalgia: How the Greeks Re-Created Their Mythical Past, from 2002, which I reference here.)
• What were the main differences between palatial Mycenaean kingdoms and the poleis?