Investment industry jargon.
Return chasers are
investors whose current investment is currently performing badly and has decided to
sell it and move into an investment that is currently peforming well. Decisions such as these are normally bad ideas. Getting out of an investment while it is down most likely means that it is sold at a
loss, which runs contrary to why someone
invests. Futhermore, buying an investment that is currently riding high doesn't mean the investor will make money.
An example would be someone owning an investment down 20%, sells it and then takes what money is left and moves into an investment up currently 30% at the time of their purchase. That person won't make a 30% return unless the investment goes up another 30% and (all together now) past performance doesn't guarantee future results.
Most of the time, these people react just to performance figures for their investment and don't think about their investment goals/objectives, the potential risks of the investment or how long they will invest for, all just as important in deciding on an investment as considering the potential return. This can also be known as performance chasing. I have heard this referred to as "driving with the rear-view mirror."