No. A 'thank you' is a colloquial compound noun, like lounge room or room heater, and the 's' in 'thank yous' signifies the plural, so no apostrophe is used. Apostrophes are used to express possession e.g. Bob's car; or

According to Answers.com, although "none" is etymologically derived from OE "one", it has been used as both a singular and a plural word from that time on as evident in the Bible, works of J. Dryden & E. Burke and many present day well known

Apostrophe ( ' ) The apostrophe is used when leaving out a letter or number in a contraction, e.g. can't, wouldn't. The apostrophe is used for omitted letters, e.g. rock 'n' roll, and for omitted numbers, e.g. the class of '72, the