Most US public libraries give free access to EBSCO’s MasterFILE Premier, which includes full-text PDFs of People, TIME, US News, and Ebony from 1975–2003.
Search: DE "Guardian Angels" AND "teenagers".
Search string to copy/paste:
"Guardian Angels" AND "teen" AND (Sliwa OR Silwa) AND magazine silwa teenager1978 to 2003magazine collection link
Direct link (example pre-filtered search):
https://archive.org/search?query=guardian+angels+teen+magazine+sliwa&and[]=mediatype%3A%22texts%22 Most US public libraries give free access to
What you’ll find: Full scans of Life, People, New York, and SPIN from 1978–1995. which includes full-text PDFs of People
If your keyword refers to Curtis Sliwa (often misspelled "Silwa"), he was a 23-year-old Bronx manager in 1978, not strictly a “teenager.” However, his Guardian Angels movement (founded February 13, 1979) was largely composed of teens aged 14–19.