This works for me, selects text with user input as BigAl suggested and MHupps first bit of code (slight modification to both, using "(getstring T....)" to allow for spaces in the text string and (cons 1 str) which mhupp uses n his second code)
(defun C:seltxt (/ SS str)
(setq str "")
(while (/= "" (setq txt (getstring T "\nType text Enter to stop ")))
(setq str (strcat str "," txt))
)
(setq SS (ssget "_X" (list '(0 . "*TEXT") (cons 1 str) (cons 410 (getvar 'ctab)))))
(sssetfirst nil ss)
(princ)
)
Noting that this is case sensitive, not sure how to do it otherwise, and it also accepts wold cards, search term Hello won't select 'Hello World' text in the drawing. but search Hello* should pick it up (and so should *llo wo*)